Welcome to C# Programming Language

Course Description

Introductory concepts of C#: development environment, variables, decisions, looping, arrays, strings, methods, exception and event handling. Prerequisite: None.

Student Learning Outcomes

By the end of this course, you should be able to do the following:

(1.) Demonstrate best practices for designing end-user computing interfaces.

(2.) Discuss software development methodologies.

(3.) Use a programming or a scripting language to solve a problem.

(4.) Discuss significant trends and emerging technologies and their impact on our global society.

Vocabulary Words

vary, variable, identifier, data type, data value, value, parameter, container, ASCII (American Standard Code for Information Exchange), static variables, instance variables, array elements, value parameters, reference parameters, output parameters, local variables, definite assignment, assignment operator, initially assigned variables, initially unassigned variables, constant, keyword, reserved keyword, contextual keyword, access keys, tab index property, type conversion, casting, cast, implicit conversion, explicit conversion, user-defined conversion, conversion with helper classes, integral numeric data types, floating-point numeric data types,

Objectives

Students will:

(1.) Discuss the meaning of variables in C#

(2.) Discuss the data types in C#

(3.) Discuss the rules for using identifiers in C#

(4.) Write C# programs involving the use of variables and data types.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) Videos: C# 101 Video Series by Microsoft
(https://channel9.msdn.com/Series/CSharp-101/?WT.mc_id=Educationalcsharp-c9-scottha)

(3.) Tutorials by W3schools: From C# Variables to C# Type Casting
(https://www.w3schools.com/cs/cs_variables.asp)

(4.) Tutorials by Microsoft - Part 1: Declare and Use Variables
(https://docs.microsoft.com/en-us/dotnet/csharp/tutorials/intro-to-csharp/hello-world?tutorial-step=2)

(5.) Tutorials by Microsoft - Part 2: From Types to Conversions
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/types)

(6.) Tutorials by Microsoft - Part 3: C# Concepts: From C# type system to Basic Types
(https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/types/)

(7.) Tutorials by Microsoft - Part 4: C# Keywords
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/)

(8.) Tutorials by Tutlane: From C# Data Types to C# Comments
(https://www.tutlane.com/tutorial/csharp/csharp-data-types-with-examples)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(9.) Type C# Variables and/or C# Data Types in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(10.) Type C# Variables and/or C# Data Types in the search bar and view/read the results.

Required Readings

A Variable is a portion of computer memory for storing a data value.
Because a variable stores a data value, it is important to identify the type of data value it stores.
This implies that any variable is associated with a data type.
The data type describes the type of data value stored by the variable.
What type of data is being stored? Are they numeric (numbers), non-numeric (letters/characters/words), etc.?
As noted with the word: variable, any value stored by it can vary (can change).
A variable is created/declared in C# by specifying the data type associated with it and assigning it to a value.
Generally, we declare a variable in C# this way:

dataType   variableName;

OR

dataType   variableName = value;

The equal sign is the assignment statement.
In other words, you assign something in C# using the equal sign.

There are seven categories of variables in C#
They are:
(1.) Static variables
(2.) Instance variables
(3.) Array elements
(4.) Value parameters
(5.) Reference parameters
(6.) Output parameters
(7.) Local variables

C# Data Types

A data type is used to define the variable.
It tells what kind of variable is being declared.
When we declare a variable or constant in a program, we must specify the type or use the var kewyord.
The var keyword means a variable keyword. Sometimes, we use it if we do not want to associate a specific data type with the variable.
Data types in C# language consists of: Value Types, Reference Types, and Pointer Types

Value Types

Let us discuss the Simple Types of the Value Types

The integral numeric data types are the: Integer, Unsigned Integer, Long, Unsigned Long, Signed Byte, Byte, Short, Unsigned Short, and Character data types.

The floating-point numeric data types are the: Float, Decimal, and Double data types.

Reference Types

...
Skip Reference Types for now
...

C# Variables

C# variables are identified with unique names known as idenfiers.
It is important to use identifiers that are meaningful and descriptive.
Anyone reviewing your program should not have to guess the meaning of your variable.

As you can see (based on the image below: Variables, Data Types, Values:)
The variables I used in that example are meaningful and descriptive
Those variables are:
state to denote the State of Ohio, OH
numState to denote the number of the State of Ohio in an alphabetical listing of the state names
povertyRate to denote the poverty rate of Ohions according to the $2000$ census data
landArea to denote the land area of the Ohio according to the $2000$ census data
motto to denote the motto and seal of the Great State of Ohio
isMottoTrue to denote the Boolean data type if the motto is true
Even without the comments, you already have an idea of the meaning of my variables.
I should not have to guess the meaning of your variables.

Naming Variables

Variable names:

(1.) Can be single letters (please avoid unless if used in loops)

(2.) Can contain a combination of letters, digits, and underscores but must not begin with a digit.
It may begin with a letter or an underscore.
It must not contain two consecutive underscores because those names are reserved for compiler generated identifiers.
Be it as it may:
(a.) Please avoid underscores
Avoid underscores even if the variable name does not begin with an underscore.
(b.) Use a combination of letters and digits such as:
num1 to represent the first number
variable1 to represent the first number

(3.) Can contain only letters but must not be any of the keywords.
C# Keywords are predefined, reserved identifiers with special meanings to the compiler.
They consist of: reserved keywords and contextual keywords

Reserved keywords have special meanings in all C# programs.

Contextual keywords have special meanings in limited C# program contexts. This means that they can be used as identifiers outside those contexts.
As new keywords are added to the C# language, they are added as contextual keywords.
This is done in order to avoid breaking programs written in earlier versions of the language.
It is highly recommended to avoid using any keywords as an identifier in any C# program.

The reserved keywords are:
abstract, as, base, bool, break, byte, case, catch, char, checked, class, const, continue, decimal, default, delegate, do, double, else, enum, event, explicit, extren, false, finally, fixed, float, for, foreach, goto, if, implicit, in, int, interface, internal, is, lock, long, namespace, new, null, object, operator, out, override, params, private, protected, public, readonly, ref, return, sbyte, sealed, short, sizeof, stackalloc, static, string, struct, switch, this, throw, true, try, typeof, uint, ulong, unchecked, unsafe, ushort, using, virtual, void, volatile, while

The contextual keywords are:
add, alias, ascending, async, await, by, descending, dynamic, equals, from, get, global, group, into, join, let, nameof, notnull, on, orderby, partial (type), partial (method), remove, select, set, unmanaged (generic type constraint), value, var, when (filter condition), where (generic type constraint), where (query clause), with, yield

(a.) The letters can be Camel case (similar to the hump of a camel) such as:
firstVariable...the V is the hump
In Camel casing letters: two letters are merged as one; the first letter of the second word is an uppercase letter while all other letters are lower case letters.
In firstVariable, V is uppercase; all other letters are lower case
(b.) The letters can be Pascal case such as FirstVariable
In Pascal casing, two letters are merged as one; the first letter of the first word and the first letter of the second word are uppercase letters while all other letters are lower case letters.
In FirstVariable, F and V are uppercase; all other letters are lowercase.
(c.) uppercase letters (please avoid...it denotes someone who is yelling)
(d.) lowercase letters (okay, but try to avoid)

Student: What if you have three words?
How do you write it in Camel case? Pascal case?
Teacher: Say we want to write the variable, first arithmetic sequence
Camel case: firstArithmeticSequence...A and S are the only uppercase
Pascal case: FirstArithmeticSequence...F, A, S are the only uppercase

In this course, for all applicable variables; please use:
(i.) A combination of letters and digits such as num1 OR
(ii.) Camel case letters such as firstNumber OR
(iii.) Pascal case letters such as FirstNumber
***We shall use single characters when we write conditions for Iteration statements/Loops because it is easier to use single characters in such cases. We shall see examples when we discuss loops. However, feel free not to use it if you wish.***

(4.) Can contain only letters but must not be these literals: true, false, null

(5.) Cannot contain whitespaces.
A whitespace is a horizontal or vertical space.
For example: myNum has no whitespace; but my Num has a whitespace.
Variable names cannot contain whitespaces.
Hence: myNum is acceptable, but my Num is not acceptable.

It is also highly recommended to avoid special characters in C# variable names.
Special characters are all the non-numeric and non-alphabet characters on your keyboard such as ~ (tilde), !(exclamation), @ (asperand), # (hash), $ (dollar), % (percent), ^ (caret), & (ampersand), * (asterisk).
For all course work, please avoid special characters in variable names.

Declaring Read-Only Variables: Use the const keyword (constant keyword)
As we have learned, a variable vary. The value changes.
However, read-only variables do not change.
Sometimes, we need these kind of variables.
We have to create/declare them using the const keyword.
For example, if we want to use the approximate value of pi as $3.142$ rather than using the exact value, we can declare it as:
const int $piValue = 3.142$
This means that the variable, piValue is a read-only variable
It will not change it's value.

Student: May you please give code examples?
Teacher: Sure.

We shall begin with console applications.
Then, we shall develop desktop applications.
We shall create a new project and name it: Module2
Let us review these two examples.



Let us try to modify the value of the read-only variable and try to run it to see the output.
Please do not run any program that compiles with an error.


As you can see, the variable $piValue2$ cannot be changed because it was declared as a read-only variable (using the const keyword)

Teacher: As you see: for the new value of piValue1, we can modify the value of any variable we create, by specifying another value for that same variable name.
Student: But, why do we need to do this?
Can't we just create another variable with that second value?
Teacher: Good point.
Yes, it is much better to create another variable with the new value.
However, when we work with statements and sorting techniques among others; it may be more efficient to just assign the new value to the same variable; rather than create another variable and assign the new value to it.
For example: if you are sorting through a loop also known as an iteration statement; we can create a variable, and write a conditional statement that when you compare an element in the array with the next element; assign the value of the greater element to the variable.
Rather than create a new variable, assign any greater value to the variable as you compare elements in the array.
There are some terms I just used, that we shall discuss in later modules.

(6.) Are case sensitive.
These are all different variables:
firstresult (lowercase),
firstResult (Camel case),
FirstResult (Pascal case),
Firstresult,
FIRSTRESULT (uppercase),
first_result (snake case)
strFirstResult (Hungarian notation)

Student: Hungarian notation?
Teacher: Hungarian notation is a naming convention that follows the camel case naming but in which the name is preceded by the data type represented by a three-character ID.
str means string
Similarly, int is for integer; dec is for decimal; dbl is for double; bln is for Boolean among others.

Variables, Data Types, Values Example: State of Ohio

Type Conversions

C# is statically-typed at compile time.
This means that after we declare a variable, that variable cannot be declared again, or assigned a value of another type unless that type is implicitly convertible to the variable's type.
For example:
(A.) You might declare the result of a calculation as an integer.
You do the calculation and the result is say $32$
However, your professor wants the answer to a double with at least one decimal place.
This means that you have to either declare the result as a double before doing the calculation, or you have to convert the integer result to a double.
And sometimes, you may need to do the latter especially if you need to use the integer result in another calculation.

(B.) You might have a float variable that you need to pass as an argument to a method whose parameter is declared as an integer.

(C.) You might need to assign a class variable to a variable of an interface type.

If you do not understand what I wrote in (B.) and (C.), do not worry.
You will understand (B.) later in this course.
You will understand (C.) in the Advanced C# course.

These kinds of operations are known as type conversions.
Type Conversions is the conversion of a variable of a data type to a different data type.
There are four kinds of conversions that can be performed in C#.
They are:
(1.) Implicit Conversion: This is the conversion of a variable from a smaller data type to a larger data type.
This is done automatically.
No special syntax is required. No information is lost.
The conversion always succeeds.
Examples include the conversions from:

                            byte to short
                            byte to char
                            byte to int
                            byte to long
                            byte to float
                            byte to double 
                            short to char
                            short to int
                            short to long
                            short to float
                            short to double
                            char to int
                            char to long
                            char to float
                            char to double 
                            int to long
                            int to float
                            int to double
                            long to float
                            long to double
                            float to double
                            derived class to base class (Advanced C# course)
                            ... among others
                        

(2.) Explicit Conversion (Casts): This is the conversion of a variable from a larger data type to a smaller data type.
It requires a cast expresson. It is done manually.
Casting is required when information might be lost in the conversion, or when the conversion may not succeed.
Examples include the conversions from:

                            double to float
                            double to long
                            double to int
                            double to char
                            double to short
                            double to byte
                            float to long
                            float to int
                            float to char
                            float to short
                            float to byte
                            long to int
                            long to char
                            long to short
                            long to byte
                            int to char
                            int to short
                            int to byte
                            char to short
                            char to byte
                            short to byte
                            base class instance to derived class  
                            ... among others 
                        

(3.) User-defined Conversion: This is the conversion that is performed by special methods that is defined to enable explicit and implicit conversions between custom types that do not have a base class-derived class relationship.

(4.) Conversions with Helper Classes: Helper classes are used to convert between non-compatible types such as integers and System.DateTime objects among others.

In this module, we shall focus only on Implicit and Explicit Conversions.
Let us demonstrate some examples.
Please review the screenshots.
Review the comments.

Implicit Conversion
Conversion from Integer data type to Double data type


Student: Mr. C, I hope you realize it did not convert the integer to double.
A double has at least one decimal place.
Teacher: It did.
However, it did not display the converted value as a double.
Student: How do we display the converted value as a double?
Teacher: Good question.
We were going to discuss it in the next module.
But, we might as well discuss it now.
We just have to round the integer to one decimal place.
One of the ways to do it is to use $F1$...format to one decimal place
Let's do it.



Explicit Conversion (Casting): First Approach
Conversion from Double data type to Integer data type


We can also perform explicit conversions using built-in methods: Convert.To data type
In using this method, please note that:
Convert.ToInt32(variable) converts the variable to an an integer
Convert.ToInt64(variable) converts the variable to an a long integer


Student: Mr. C, what if I want to use the Second Approach with the built-in method?
But I want to use more than one variable.
The system is giving an error when I declare the variable (the converted variable) as an integer
Kinda wonder how you were able to print it without declaring it.
Teacher: This is one of the reasons why I prefer this approach.
You can just print it without having to declare a new variable, assign to it, and print.
Student: I know.
But if I want to use a new variable with it, is that possible or not?
Teacher: It is possible.
Remember we mentioned the var keyword at some point.
This is an example of a case where we use it.
Let's try it.



Student: Can we also use this approach for the Implicit conversion?
Teacher: Yes. It works for implicit conversions too.
Student: I guess it is just better to use this approach for both implicit and explicit conversions.
Because one might not know the data types that can be converted implicitly because of the long list
Teacher: The IDE will typically inform you if a specific conversion is permissible, and probably give you recommendations on what to do.
You are always welcome to use this approach.
Let us discuss the approach that works for both implicit and explicit conversions.
I prefer using this approach.

Implict and Explicit Conversions

Convert.To (data type) method
This is a method of the Convert Class from the System namespace
It converts a base data type to another base data type.

GUI Programming: Electronic Flashcards with C#

As usual, we shall develop desktop applications that involves the use of variables and data types.
Let us develop desktop applications for the console application we did for the State of Ohio
We shall use several toolboxes.
Remember that the Midterm Project is a desktop application.
Hence, it is necessary to start getting familiar with GUI programming.
Please review the desktop application we did in Module $1$
We shall give appropriate names for our projects.

First Flashcard: Variables and Data Types: Labels and Buttons

Tasks:
User Interface and Properties

Form:
Name Property: Leave as is
Text Property: State of Ohio: Labels and Buttons
BackColor Property: Web: Wheat
Font Property: Font: Times New Roman; Font style: Regular; Size: $14$; Script: Western

Select the first label on the left: the State label (Text property); hold the CTRL key on your keyboard and select all the Left Hand Side (LHS) labels


Aligh all the LHS labels to the left


Click on an empty space in the form to deselect all the RHS labels.
Select the first label on the right: the StateLabel (Name property); hold the CTRL key on your keyboard and select all the Right Hand Side (RHS) labels


Aligh all the RHS labels to the right


Click on an empty space in the form to deselect all the RHS labels.
Select the three buttons.
Click the Format menu, Make Same Size: Both


Click on an empty space in the form to deselect the three buttons.

Student: Mr. C
I have a question.
Why did you decide to include that symbol besides the "C" in the Clear button and the "x" in the Exit button?
Teacher: Very good question.
That symbol is known as the ampersand symbol
The underlined word is known as an Access Key
Student: What is an Access Key?

Graphical User Interface (GUI) Design: Access Key

(1.) An Access Key is a key assigned to an object (toolbox control objects) by including the ampersand symbol, & before a letter or number in the Text Property of the object.

(2.) When you run any desktop application, press the Alt key
If access keys were used in the application, you will see the underlined letter.
Any user can access the application by using a combination of the Alt key and the Access key to select the specific object.
For example in our program: when we run the application; a combination of Alt + C clears the entries in the application.
Similarly, Alt + X combination selects the Exit button and exits the application.

(3.) Access keys are useful for those who cannot work with a mouse, or who do not want to work with a mouse.

(4.) It is important for programmers to assign access keys to objects that accept user input such as TextBoxes and to objects that perform actions such as buttons.
It is part of Accessibility Design for people with disabilities.
The use of access keys in the Midterm Project is required.
It is important to use meaningful access keys.

(5.) Pressing the Alt key temporarily shows the accessing keys.

(6.) Access keys are not case sensitive.

(7.) Toolbox controls that cannot receive focus cannot have access keys.

Code our Program (Write the Program Code)

(1.) Go to the Design View of the form and double click the State of Ohio button

(2.) Declare the variables

(3.) Write the code.

(4.) Alternatively, you can go to the View menu, and view Code
Then, select the OhioButton in the Code View under the Form1() dropdown list.

(5.) In the same manner, code the Clear button and the Exit button

(6.) Build Solution

(7.) Run the program.

Please view the screenshots. Study the comments and the code.

Clean up your code.
Remove unused events.
If you have any unused event in the Code window, take these steps to remove it.
Remove each event one at a time.
Remove the first one.
Go to the Design window and you will see an error.
Click the main line (the error)
The Designer window opens and the error line is indicated.
Delete that error line.











The TextBox is a Windows control that:
(1.) Accepts user input.
It accepts only the string type by default. So, if we want to use numeric types say an integer; then we need to convert the string to an integer using the Convert.ToInt32 method or the Int32.TryParse method.
The TextBox can also be used to display user input. It displays only strings by default.
So, if we want to use the TextBox to display a numeric type say a double; then we need to include it in a string interpolation or use the ToString() method.

(2.) Provides MultiLine editing with vertical scroll bars.
To use this feature, we have to check the box: MultiLine when we drag the TextBox into the form.

The Label is a Windows control that:
(1.) Provides descriptive text for a control.
(2.) is also used to display the program output.
It displays only strings by default.
So, if we want to use the Label to display a numeric type say a double; then we need to include it in a string interpolation or use the ToString() method.
The AutoSize property needs to be set to False so the label can be expanded.
In addition, I prefer to set the BorderStyle property to Fixed3D.

The Button is a Windows control that raises an event when a user clicks it (click event).
In other words, it performs an action when clicked.

Second Flashcard: Variables and Data Types: RichTextBox and Buttons

Here, we shall use the RichTextBox and the Buttons. No labels.

The RichTextBox is a toolbox control that:
(1.) Accepts user input.
It accepts only the string type by default. So, if we want to use numeric types say an integer; then we need to convert the string to an integer using the Convert.ToInt32 method or the Int32.TryParse method.
The TextBox can also be used to display user input. It displays only strings by default.
So, if we want to use the TextBox to display a numeric type say a double; then we need to include it in a string interpolation or use the ToString() method.

(2.) Provides MultiLine editing with vertical scroll bars.

Tasks:
User Interface and Properties

Form:
Name Property: Leave as is
Text Property: State of Ohio: RichTextBox and Buttons
BackColor Property: Web: Cornsilk
Font Property: Font: Times New Roman; Font style: Regular; Size: $14$; Script: Western

Select the three buttons.
Click the Format menu, Make Same Size: Both (as we did in the first flashcard)

Code our Program (Write the Program Code)

(1.) Double click the State of Ohio button

(2.) Declare the variables

(3.) Write the code.

(4.) Code the Clear button and the Exit button

(5.) Build Solution



(6.) Run the program.

Please view the screenshots. Study the comments and the code.

We shall explore more toolbox controls in subsequent modules.

Some Substantive Posts

(1.) Using at least five complete sentences and at least five different variables and data types, write a program of the summary of what you learned in this module.

(2.) Write a program of a short story, a poem, or drama using at least five sentences and at least five different variables and data types.

(3.) Write a program that displays examples of all the Value data types and the string data type.

(4.) Write a program that demonstrates at least ten examples of Implicit Type Conversions
Use the data types listed in this Module.

(5.) Write a program that demonstrates at least ten examples of Explicit Type Conversions
Use the data types listed in this Module.

(6.) Write a program of a short story, a poem, or drama using at least five sentences, the same variable, and at least three different data types.

(7.) To be done by only one student on a first-come first-served basis
Assume you have three initials.
Write a program that declares variables to hold your three initials.
Display the three initials with a period following each one, for example: $S.D.C$

Some Substantive Responses

(1.) Provide any of these details if they are lacking in any DB post:
Well-written comments; another approach/method to solving the question; any additional relevant details; etc.

(2.) Review the post (Discuss Questions and Assess Questions) done by your colleagues.
If your colleague developed a console application for a program, develop a desktop application for the same program.
If your colleague developed a desktop application for a program, develop a console application for the same program.

(3.) Other substantive responses.

Check Your Understanding

(1.) Develop a Graphical User Interface (GUI) of a short story, a poem, or drama using at least five sentences and at least five different variables and data types.
At least three buttons: the button that displays the information, the Clear button and the Exit button should be included.
Include access keys for the three buttons.

(2.) Develop a Graphical User Interface of a short story, a poem, or drama using at least five sentences, the same variable, and at least three different data types.
At least three buttons: the button that displays the information, the Clear button and the Exit button should be included.
Include access keys for the three buttons.

(3.) Develop a GUI flashcard of all the Simple Types of the Value Types and the string data type.
A brief definition of each data type should be displayed when the user performs an event (such as pointing the mouse or clicking) on each data type.
Use whatever toolbox controls you prefer.

Vocabulary Words

number, variable, constant, literal, value element, operator, operand, operation, expression, arithmetic operators, assignment operators, comparison operators, conditional operator, tenary conditional operator, Boolean logical operators, bitwise and shift operators, equality operators, member access operators, member access expressions, type-testing operators, cast expression, user-defined conversion operators, pointer-related operators, null-forgiving operator, null-coalescing operator, lambda operator, scope resolution operator, namespace alias qualifier, await operator, delegate operator, New operator, Sizeof Operator, unary operators, binary operators, increment operator, decrement operator, plus operator, minus operator, multiplication operator, division operator, remainder operator, addition, operator, subtraction operator, prefix increment operator, postfix increment operator, prefix decrement operator, postfix decrement operator, compound assignment, operator precedence and associativity, arithmetic overflow, division by zero, round-off errors, floating-point division, operator overloading, access keys, TabIndex property, ComboBox, MessageBox, calculator, MaskedTextBox control, NumericUpDown control, KeyPress event, regular expressions (regex)

Objectives

Students will:

(1.) Discuss the operators in C#
(2.) Perform operations on variables/values
(3.) Write C# programs involving the use of operators.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) C# Operators and Expressions: From: Overview To: Operator Overloading by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(3.) Type C# Numbers and/or C# Operators in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(4.) Type C# Numbers and/or C# Operators in the search bar and view/read the results.

These references will be useful as we progress through the course:

(5.) List of C# Math Functions
(https://docs.microsoft.com/en-us/dotnet/api/system.math?view=net-5.0)

(6.) Format Types in .NET
(https://docs.microsoft.com/en-us/dotnet/standard/base-types/formatting-types)
.NET means that the format types are applicable to C# and C#

(7.) Standard Numeric Format Strings
(https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings)

Operators

Operators are special symbols that perform specific operations on one or more operands, and returns an output.
An Operand is the variable/value on which an operation is done.

An expression is a series of value elements combined with operators, which yields a new value.
Value elements include variables, constants, literals, properties, returns from Function, and Operator procedures, and expressions.

The operators act on the value elements by performing calculations, comparison, or other operations.

The types of operators in C# are:
(1.) Arithmetic Operators
(2.) Assignment Operators
(3.) Comparison Operators
(4.) Conditional Operator
(5.) Boolean Logical Operators Please review Module 4 for the examples
(6.) Bitwise and Shift Operators
(7.) Equality Operators
(8.) Member Access Operators and Expressions
(9.) Type-testing Operators and Cast Expression
(10.) User-defined Conversion Operators
(11.) Pointer-related Operators
(12.) Null-forgiving Operator (!)
(13.) Null-coalescing Operator (??)
(14.) Lambda Operator (=>)
(15.) Scope Resolution Operator (::) (known in C# as Namespace alias qualifier)
(16.) Await Operator
(17.) Delegate Operator
(18.) New Operator
(19.) Sizeof Operator

Let us discuss some of these operators.

Arithmetic Operators

Arithmetic Operators are used to perform arithmetic operations with operands of numeric types.
They are grouped into Unary operators and Binary operators

The Unary operators are the:
(1.) Increment operator (++)
These consists of the Prefix Increment and the Postfix Increment operators
The prefix increment say: x++ is the value of x after the operation.
The postfix increment say: ++x is the value of x before the operation.

(2.) Decrement operator (--). These consists of the Prefix Decrement and the Postfix Decrement operators
The prefix decrement say: x-- is the value of x after the operation.
The postfix decrement say: --x is the value of x before the operation.

(3.) Plus operator (+)

(4.) Minus operator (-)

The Binary operators are the:
(1.) Addition operator (+)

(2.) Subtraction (-) operator

(3.) Multiplication (*) operator

(4.) Division (/) operator

(5.) Remainder or Modulus operator (%): This is the integer remainder after a division.

Let us demonstrate some examples of Arithmetic operators.
Please review the screenshots and the comments.

Unary Arithmetic Operators





Student: Mr. C, how did you underline the words in the Console window?
The codes you used...
Teacher: Yes, the codes underline words in the Console window
They work for C# and C++ console window applications
You can also add foreground and background colors.
This is the List of the Console Log Formatting Commands
(https://www.samdomforpeace.com/References/ASCII.html#console)
\x1B[4m command underlines the text in the console.
\x1B[0m command resets it (closes the underlined text).
It is important to reset it, else it will underline the entire text in the console.
If you add foreground and background colors, it is also important to reset.
Notice that for C# (in that website), you can use the commands for (VB and C#) or you can use the commands for (C# and C++), whichever you prefer. You can use both if you like.

Binary Arithmetic Operators



Teacher: Notice what we did for the division?
It is necessary for the result to be displayed as a double data type.

Let us solve more examples.
Please visit my website on Numbers
(www.numbersandnotations.appspot.com/numbers.html)
Let us solve Questions $10$, $6$, $7$, and $23$ on that website
We shall use only Arithmetic Operators to solve Question $10$
We shall cover Functions (Methods) in Module $6$. However, it is important to introduce you to C# Math Functions in this module because we are dealing with Numbers in this module.
We shall use Arithmetic Operators and C# Math Functions to solve Questions 10, 6, 7, and 23
This is the List of C# Math Functions
(https://docs.microsoft.com/en-us/dotnet/api/system.math?view=net-5.0)
Please review the screenshots and the comments.




Teacher: You know one of the things I like about C#?
Student: What?
See how we declared the answers as double data type
But if the answer is an integer, C# displayed the answer as an integer rather than as a double
Java would have "messed" this up...displaying it as a double, then we have to convert that double back to an integer
With C#, when we declare the answer as a double; if the answer is an integer, it will display it as an integer.
If the answer is a double, it will display it as a double.
Student: I like that too
Teacher: Yep...
But we need to declare it as a double because a double is a larger data type.
If we declare it as an integer and the answer is a double, then it will be rounded...that is not what we want.
Student: Look at Question (7.)
The answer on your website is not "exactly" the same as the answer displayed by the program
$84.7$ is not really $84.69999999999999$
Teacher: Good observation
The double data type has a double-precision floating point.
Hence, sometimes, it does not give the perfect accurate exact answer.

Assignment Operators

Assignment Operators are used to assign a value to a variable or property.
The equal sign is the assignment operator for programming languages (not just for C#)
Compound Assignment Operators are used to perform an operation on the value of a variable before assigning an updated value to the variable.
They are:
$=$ operator (assignment operator)
$+=$ operator (compound assignment: add before assignment)
$-=$ operator (compound assignment: subtract before assignment)
$*=$ operator (compound assignment: multiply before assignment)
/= operator (compound assignment: divide before assignment)
\= operator (compound assignment: integer division before assignment)
^= operator (compound assignment: raise to an exponent before assignment)
≪ $=$ operator (compound assignment: arithmetic left shift before assignment)
≫ $=$ operator (compound assignment: arithmetic right shift before assignment)
&$=$ operator (compound assignment: concatenate a string expression to a string variable before assignment)
We use compound assignment operators if we want to do two things in one.
Rather than perform two tasks using two steps, perform those two tasks using one step.
Some people like it. Some people do not.
However, I prefer you learn it because you will most likely find it useful when we cover Statements in Module $5$
Let us demonstrate what I mean.
Please visit my website on Percent Applications
(www.fractions-decimals-percents.appspot.com/percentApplications.html)
Let us solve Question $1$ on that website
Because this calculation deals with currency (money), we shall use the currency format specifier
The advantage of using the currency format specifier is that it rounds the value to two decimal places (money/currency is rounded to two decimal places) and it also includes the currency.
These are the Format Types in .NET
These are the Standard Numeric Format Strings
Let us format the result display in the console.
Please review the screenshots and the comments.




Student: Mr. C, I do not want to be confused by what you do.
Teacher: What is it my dear?
Student: You put the d in the first approach.
But you did not put the d in the second approach.
That is confusing...you do something for one and you do not do the same thing for another.
Teacher: I understand.
It is recommended that you put d when you declare a double data type for a variable.
However, by default; any decimal in C# is seen as a double data type.
That is also another reason to use the double data type rather than the float data type.
The first reason is because of the precision.
Another reason is that any decimal number in C# is a double data type by default.
So, if we forget to include the d after the decimal, that is not a problem.
It is better to include it.
But, it is not a problem if you forget to include it.
Student: Okay.
What if I write: const float serviceTip = 0.12
Will it work?
Teacher: No, it will not work because the decimal number is a double data type in C# by default.
If you want to use a float for that, you will need to include the f after the decimal number
Like const float serviceTip = 0.12f will work as a float.
However, keep in mind that the rest of the variables will have to be floats as well.
Otherwise you will have to convert them to floats.
It is much better to use the double data type.
Nice observation!

Comparison Operators

Comparison operators are operators that compare two operands and return a Boolean value.
The operands can be single values or expressions containing several values (enclosed in parentheses).
The operands can be numeric values, strings, and objects.
The Boolean value represents the relationaship of their values.
They are also known as Relational operators.
They include the:
$==$ (Equality) operator
$!=$ (Inequality or Not Equal) operator
< (Less than) operator
> (Greater than) operator
<= (Less than or equal to) operator
>= (Greater than or equal to) operator
Let us discuss Comparison operators.

Operator Precedence and Associativity

Input/Output Feature

One of the nice features of the C#langauge is the Input/Output feature.
This feature is interactive.
You use this input/output feature in several applications.
A common application is an application that verifies one's identity by inputting the first name, last name, date of birth, etc.
To use the Input/Output feature, the Console.ReadLine() method is used.
Remember we discussed the Console.ReadLine() and the Console.ReadKey() methods in Module $1$. Please review Module $1$
Console.ReadLine() method reads the next line of characters from the standard input stream.
It reads strings.
Console.ReadKey() method: obtains the next character or function key pressed by the user.

We also have:
Console.Read() method: This method reads the next character from the standard input stream.
We shall cover Functions in Module $5$. For now, let us just stick with the Console.ReadLine() method.

Let us demonstrate the input/output feature with numbers so we see how it works.
Please review the screenshots and the comments.

Input/Output Feature: Example $1$
Let us solve Question $12$ on the Numbers website.




Input/Output Feature: Example 2
Let us do a real-world application for this example.
Onto the ...

Application: BMI (Body Mass Index)

Please review the BMI information on these two government websites [from the Center for Disease Control and Prevention (CDC) and the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH)]
About Adult BMI | Healthy Weight, Nutrition, and Physical Activity | CDC and
Calculate Your BMI - Standard BMI Calculator

As at today, the 3rd day of September, 2020; the BMI information on both websites are:

NIH website
Calculate Your BMI - Standard BMI Calculator


CDC website
About Adult BMI | Healthy Weight, Nutrition, and Physical Activity | CDC

Formula for Calculating Body Mass Index: United States System (Customary System)

$ BMI = \left(\dfrac{weight}{height * height}\right) * 703 \\[5ex] weight\:\:is\:\:in\:\:pounds (lb) \\[3ex] height\:\:is\:\:in\:\:inches (in) $

Formula for Calculating Body Mass Index: International System (Metric System)

$ BMI = \left(\dfrac{weight}{height * height}\right) \\[5ex] weight\:\:is\:\:in\:\:kilograms (kg) \\[3ex] height\:\:is\:\:in\:\:meters (m) \\[3ex] $ If you need help with conversion of units, please review the Tables and Examples in Measurements and Units

Teacher: What do you notice in both websites?
Student: They both have the information on the BMI.
In addition, the CDC website has information for both Adult BMI and Child & Teen BMI among others.
The NIH website has recommendations among others.
Teacher: That is correct. What else?
Student: They have the BMI calculator.
Teacher: Did you notice any difference in the calculator on both websites?
Student: The NIH website has BMI calculator for both Standard and Metric versions.
The CDC website has the BMI calculator for only the Metric version.
Teacher: Did you notice any issue/concern about the BMI information?
Student: Not really. Why?
Teacher: So, this is what we are going to do.
Let us develop the BMI calculator.
That calculator will calculate the BMI.
Then, we shall interpret that BMI, and make a recommendation.
. The CDC website gave us the formula for calculating the BMI. So, we shall use it.
As you can see, our calculator would have to use conditional statements for the interpretation and recommendation.
But, here is the issue.
Student: Wait, I think I see the issue.
The issue is with the domains.
Teacher: Correct!
Anyone having a BMI between $18.5$ and $24.9$ both endpoints included has a Normal weight.
This is: Normal weight: [18.5, 24.9]. It is a closed interval (relate with Mathematics).
So, the Overweight range for the BMI should be the weight greater than $24.9$, (rather than beginning from $25$) and ending at $29.9$
For the Overweight range, the first endpoint is not included, but the second endpoint is included.
This is: Overweight: (24.9, 29.9]. It is a half-open half-closed interval (relate with Mathematics)
Teacher: Do you know why this would be a problem if the programmer does not fix these issues before developing the calculator?
Student: Yes. Because there would not be any interpretation for anyone whose BMI is between $24.9$ and $25$
But, I do see that the BMI information is for values rounded to one decimal place.
Teacher: That is correct.
And we shall develop our calculator to round to one decimal place.
But, it is important we fix the issues.
What if we do not want to round?
Look at the two examples on the CDC website. The BMI values were rounded to two decimal places.
If we developed our calculator to round to two decimal places with the information on those websites "as is"; then we would not have the interpretation and recommendation for those two examples ($24.98$ and $24.96$) because those values are greater than $24.9$ but less than $25$.
Student: That makes sense.
So, the last one: Obese should be BMI greater than $29.9$, rather than greater than $30$?
Teacher: That is correct.

Let us apply what we learned so far.
We shall develop a console application and a desktop application for the Body Mass Index (BMI) calculator.
I do the console application.
You do the desktop application.
We are yet to cover Statements (covered in Module 5). However, do not worry.
I explained my comments very well. You will understand the comments.
Please ask questions if you do not understand any of the comments.
We shall use part of Module $5$ (Decision-making statements) in the program.
Please review the screenshots and the comments.

(1.) The program should accept user inputs of:
(I.) First name
(II.) Last name
(III.) Weight
(IV. Height

(2.) The program should output the:
(A.) BMI value
(B.) Interpretation
(C.) Recommendation

(3.) The program should address user-input errors of non-positive numbers for the weight and the height.
Inform the user.
Then, exit the program. Do not allow the program to continue.
To exit the program, we use the command: Environment.Exit(0); or Application.Exit();
Conditional Logical AND in C# is represented by the double ampersand symbol &&
Conditional Logical OR in C# is represented by the double pipe symbol ||

Student: I have several questions, Mr. C
Teacher: Please go ahead
Student: First Question: Why did you initialize those variables?
The interpretBMI and the adviceBMI...you initialized them to String.Empty
Teacher: Good question.
Assume we did not initialize them
We only defined them within the block of code: the If Statement
Then, we want to print them/output them outside the block of code
The program "will not be happy"
Compare it to this scenario.
A student registered to attend a school.
We did not register the student at the front office registration desk.
But we sent the student to a classroom and the classroom teacher registered that student.
The parents come, looking for their child.
Where will the parent go first?
Student: At the front desk of course
Teacher: Good.
The front desk will first keep a record of the student before sending the student to the class.
We have to first assign the string to something before we send it to the blocks of code, and then output it.
We cannot just declare it without an assignment, then send it to a block of code to be used within that block of code only, and then want to output it outside the block of code.
Does it make sense?
Student: Yes, it does.
But what if we do not want to print the value outside the block of code?
What if we want to print the value inside each block of code where it is used?
Teacher: I am impressed by your questions.
Yes, we can do that.
But you know what that means...right?
Student: We have to write it each time for each of the conditional statement.
Teacher: That is correct.
Student: Second Question: Why did you underline the 0 on the console window?
....process exited with 0?
Teacher: Unless defined in the program otherwise; anytime you run a program and the program exited with 0, it means that the program successfully exited.
0 basically lets you know that the program ended successfully.

Graphical User Interface (GUI) Design: User-input for Numeric Data Types

A very important concept of software design is to plan for user-input errors.
Every user is not expected to know how to use your software.
Have you read/seen events where a child gets the parents iPad and purchases applications (apps) without their consent/approval; and funny enough, when the child does not even that he/she purchased those apps?
Maybe the parents should enable some authentication factors before apps are purchased.
Maybe Apple should not store the debit/credit card information on the device.
Well, considering the fact that the two main goals of every business (including non-profit organizations) is to: Maximize profit and Minimize cost; the second "Maybe" is unlikely.
Be it as it may; we want to address user-input errors in any software we design: console application, desktop application, web application, and mobile application.
For example: for the Midterm Project in Module 5; say you did an application that involves the user to enter in the Tax percentage, we know the tax cannot be negative.
So, you can prevent the user from entering a negative number (preventing an error in the final result) or you can notify the user that a negative number is not allowed.

Addressing user-input errors includes:
(1.) Prevent errors: Prevent the user from making an error.
For example: If you want the user to enter only positive integers in a specific TextBox, design the software in such a way that the TextBox will not accept nonpositive integers (zero and negative integers).

(2.) Handle errors: also known as Error Handling or Exception Handling
Handle any error made by the user.
The Visual Studio IDE throws an exception (error) in some cases. We shall discuss these kinds of exceptions in the Advanced C# course.
However, it is important to handle those errors overlooked by Visual Studio.
An example is the code we wrote in Lines #73 - #77 and Lines #80 - #84 (though we wrote it for console application)
We can write similar code for desktop applications.

Let us discuss some approaches to preventing errors when working with numeric data types.
They are:
(1.) MaskedTextBox control
(2.) NumericUpDown control
(3.) TextBox control using KeyPress event with Regular Expressions

MaskedTextBox Control

The MaskedTextBox uses a mask to distinguish between proper and improper user input.

A Mask is the default property for the MaskedTextBox
It is a string (because TextBoxes accept only strings) composed of one or more masking elements. (Please see the table for the masking elements)





As you notice from the last screenshot, there are System predefined masks for phone numbers, social security number, date, time, and zip code.
However, we can select our define our own mask (custom mask).
The System predefined masks are the ones I recommend.
I do not recommend the use of custom masks unless your professor says otherwise.
Nevertheless, let us discuss it, should you find them useful for your personal projects.
We define custom masks based on these descriptions.

Let us review some examples of the MaskedTextBox for Numbers.

Form1.cs: Adjust and Align
(Name) property: Leave as is. Do not change
Text property: Numbers Validation: MaskedTextBox
BackColor property: Web: Biege
Font: property: Font: Times New Roman;     Font Style: Regular;     Size: 18
FormBorderStyle property: Fixed3D
MaximizeBox property: False

Set Properties for the Toolbox Controls

Toolbox Controls	Property
Label: Adjust and Align	Text: Age (years):
MaskedTextBox: Adjust and Align	(Name): YearsMaskedTextBox
Label: Adjust and Align	Text: Nonnegative Integers only
Teacher: Let us set the property for the MaskedTextBox Have you seen anyone that is more than $3-digits$ in age? Student: No, Mr. C The oldest man that ever lived is Methuselah. He was 969 years old. And that is three digits. Teacher: Okay, let us set the MaskedTextBox for Age. Let us set it to three digits. However, we will make it optional. This means that we shall use $999$ rather than $000$ Student: So, the user cannot enter any negative number in that MaskedTextBox? Teacher: That is correct. It prevents the user from entering a negative number or from entering a string. Only a one-digit, tw0-digit, or three-digit nonnegative integer is allowed. Let us review more examples.
Label: Adjust and Align	Text: Account (in red): ForeColor: Web: Red
MaskedTextBox: Adjust and Align	(Name): RedAccountMaskedTextBox Mask: ####.## (for $-120.55$)
Label: Adjust and Align	Text: $\$$
Label: Adjust and Align	Text: Negative Decimals
Label: Adjust and Align	Text: Account (in green): ForeColor: Web: Green
MaskedTextBox: Adjust and Align	(Name): GreenAccountMaskedTextBox Mask: ###.## (for $120.75$)
Label: Adjust and Align	Text: $\$$
Label: Adjust and Align	Text: Nonnegative Decimals
Button: Adjust and Align	Name: DemoButton Text: Demonstrate BackColor: Web: White

We use the MaskedTextBox just as we use the TextBox (it is a TextBox anyway, just that it is masked).
All the user-input in a TextBox (including the MaskedTextBox) are treated as strings.
So, we will need to convert it to a numeric data type, use the numbers, and then reconvert back to string using String Interpolation or the ToString() method in order to display it in a Label or MessageBox.
We have used labels in previous applications.
Let us use a MessageBox this time.
Let us demonstrate the MaskedTextBox with a Button and a MessageBox.
A MessageBox displays a message box.
The MessageBox accepts only strings. Hence, we need to use the String Interpolation (my preference) to display those values as strings.
A frequently-used method of the MessageBox is the MessageBox.Show() method.
(https://docs.microsoft.com/en-us/dotnet/api/system.windows.messagebox.show?view=net-5.0)

NumericUpDown Control

The NumericUpDown control displays a single numeric value that the user can increment (by clicking the Up arrow key on the control) or decrement (by clicking the Down arrow key on the control)
Alternatively, the user can type a number in the box part of the control.
The control displays and sets a single numeric value from a list of fixed numeric-value choices.
It is a good choice for creating a volume control for a music player application.
Let us review some examples of the NumericUpDown for Numbers.

Form1.cs: Adjust and Align
(Name) property: Leave as is. Do not change
Text property: Numbers Validation: NumericUpDown
BackColor property: Web: SeaShell
Font: property: Font: Times New Roman;     Font Style: Regular;     Size: 18
FormBorderStyle property: Fixed3D
MaximizeBox property: False

Set Properties for the Toolbox Controls

Toolbox Controls	Property
Label: Adjust and Align	Text: Age (years):
NumericUpDown: Adjust and Align	(Name): YearsNumericUpDown
Label: Adjust and Align	Text: Nonnegative Integers only
Teacher: Let us set the property for the YearsNumericUpDown Rather than use 999 that we used in the MaskedTextBox, let us: Leave DecimalPlaces property: 0 "as is" Set: Increment property: 1 "as is" because the age of someone increases by 1 Set: Maximum property: 999 Set: Minimum property: 0 because someone can be 0 years and some months
Label: Adjust and Align	Text: Age (months):
NumericUpDown: Adjust and Align	(Name): MonthsNumericUpDown DecimalPlaces: 0 Increment: 1 Maximum: $999 * 12 = 11988$ Minimum: 1 (because someone's age cannot be zero months)
Label: Adjust and Align	Text: Positive Integers only
Label: Adjust and Align	Text: Account (in red): ForeColor: Web: Red
NumericUpDown: Adjust and Align	(Name): RedAccountNumericUpDown DecimalPlaces: $2$ Increment: $0.01$ Maximum: $-0.01$ Minimum: $-1000000000.00$
Label: Adjust and Align	Text: $\$$
Label: Adjust and Align	Text: Negative Decimals only
Label: Adjust and Align	Text: Account (in green): ForeColor: Web: Green
NumericUpDown: Adjust and Align	(Name): GreenAccountNumericUpDown DecimalPlaces: $2$ Increment: $0.01$ Maximum: $1000000000.00$ Minimum: $0.01$
Label: Adjust and Align	Text: $\$$
Label: Adjust and Align	Text: Nonnegative Decimals only
Button: Adjust and Align	Name: DemoButton Text: Demonstrate BackColor: Web: White

The NumericUpDown control accepts numeric data types (decimal, floating point types, and integral types)
However, it displays only the decimal by default (because of the DecimalPlaces property which must have a value)
This implies that in order to display any data type that is not a decimal, a conversion is required.
For example: to display a value as an integer, an explicit conversion (casting) is required because the decimal type is the larger data type. (decimal is larger than an integer)
To display a value as a double, an implicit conversion is required because the decimal type is smaller data type (decimal is smaller than a double)
If you do not want to convert, then you have to declare the variable as a decimal type.
Let us implement a NumericUpDown control







Teacher: Do you understand what I did in Lines #38 and #40?
I wanted to "mess things up" a little bit. I hope it did not confuse you.
I used a String Interpolation. However, I did not want to use the currency format specifier to display the currencies like I did for the MaskedTextBox
Line #38: Will display the dollar symbol though I did not use the currency format specifier
Line #40: Had to convert the decimal to double before adding it to the other double and then used the currency format specifier to express the balance.

TextBox Control using KeyPress event with Regular Expressions

We shall discuss these approaches with the String data types in Module $4$

Teacher: Would you rather prevent errors or handle errors?
Student: I would prevent them.
It's better that way.
Teacher: True. But some errors may not be preventable.
Hence, we still need to know how to handle them.
Student: Can you give an example of a non-peventatble error?
Teacher: I'm just saying (speaking like an American lol)
For example: let's say in the Midterm Project (which is a Piecewise Function application)
Let's say you were doing an application on Power Rates
A user may input a final reading that is less than the initial reading
And the user may input it intentionally or unintentionally
Student: But can we not find a way to use any of these approaches and prevent it?
Teacher: We can.

GUI Programming: Develop a Standard Calculator with C#

Let us make a note of an important concept: Property Names of the Toolbox Controls
Notice the three dots in this screenshot image (indicated by the arrow):


Whenever you notice something like that anywhere in your code, it is important to point your mouse at it and click the Show potential fixes link:



Notice the issue was a naming rule violation. It is not a "big" issue hence those three dots.
It is not a warning. It is not an error. But it is a violation.
You do want to ensure your project is free of all violations (not just warnings and errors).
So, let us address that naming rule violation.


Going forward, we shall name each property of any toolbox control using Pascal casing.
Let us apply the knowledge we acquired in this module to develop a desktop application.
Which application comes to mind right away...a desktop application that deals with Numbers and Operators?
It's the Standard Calculator. Let's develop it. 😊
Please review the desktop applications we developed in previous modules beginning from Module $1$

Let us begin with the desktop calculator on your Windows PC/Laptop
Please see the screenshots




Let us develop the function buttons as seen in the red rectangle.

We are yet to cover Statements (covered in Module $5$). However, do not worry.
I explained the comments very well. You will understand the comments.
Please ask questions if you do not understand any of the comments.
We shall use part of Module $5$ (Conditional statements) in the program.

First Calculator: Standard Calculator: Label, TextBox and Buttons

Design User Interface and Set Properties

Form1.cs: Adjust and Align
(Name) property: Leave as is. Do not change
Text property: Standard Calculator © 2021 SamDom4Peace Designs (Sample)
BackColor property: Web: SeaShell
Font: property: Font: Times New Roman;     Font Style: Regular;     Size: 18
FormBorderStyle property: Fixed3D
MaximizeBox property: False

The MaximizeBox property is set to False if we do not want the user to maximize the application.
The reason is because we want the interface to have a consistent look.

Code our Program (Write the Program Code)

(1.) Double-click the $1/x$ button in the Design window.
This leads to the Code window
Scroll a little bit to the top, write the comments, and begin to...

(2.) Write the code.
Let us use a top-down approach.
Double-click each button in the Design window to open the Code window.
Then write the code for the event: what should happen when the user clicks the button?
Please review the screenshots.
Review the comments.

Design Area
Access keys: C for the Clear and x for the Exit buttons


Program Code





















Run the Program






$\infty$ means Infinity













NaN means Not a Number
It is not a real number.
But it is an imaginary number.
It is covered under Complex Numbers in Algebra)
This calculator deals with only with real numbers.











$-\infty$ means Negative Infinity




Functionalities of the Calculator
(1.) For operation involving two numbers: the calculator works for any positive numbers
(2.) For operation involving two numbers: the calculator works if the first number is negative
(3.) For operation involving one number: the calculator works for any number
(4.) For any operation: the user sees what he/she did
(5.) Division of a number by zero and the square root of a negative number is handled.

Limitations of the Calculator
(1.) For operation involving two numbers: the calculator does not work for two negative numbers
(2.) The calculator computes one operation at a time. It does not do multiple operations simultaneously

Second Calculator: Scientific Calculator: ComboBox, TextBox, Label, and Button

Design User Interface and Set Properties

Let us design another calcuator using more toolbox controls.
For this calculator:
(1.) We want two TextBoxes for user-input.
The two TextBoxes will receive user-input for two numbers (the operands).
Remember that TextBoxes accept only strings.
But we want them to accept numbers.
We shall define those numbers using the double data type (to accomodate decimals).
Then, we shall convert those numbers as strings so that the TextBoxes will accept them.

(2.) We want a ComboBox.
The ComboBox will contain a dropdown list of items: the operations.
We shall expand our list of operations. So, this calculator will be more of a scientific calculator.
I shall do some functions.
You do the rest of the functions (just as we did for the Standard Calculator).
We shall use an access key with the ComboBox.

(3.) We want four buttons: the Calculate, Clear Some, Clear All, and Exit buttons.
We shall use access keys with these buttons.

(4.) When we run our program, we want the cursor to be focused on the first TextBox.
Then, we want the user to be able to use the Tab key on the keyboard to perform any operation without using a mouse.
This is an important software design concept to accommodate users with disabilities.
Access keys is one of the ways to work only with the keyboard keys.
Another way is the TabIndex Property.
Once the user enters the first number in the first TextBox; move to the ComboBox and select an operation from the dropdown list and press the Tab key; use the Tab to move to the second TextBox (as applicable), enter the second number and press the Tab key (as applicable); move to the Calculate button and hit the Enter key to get the result.
The TabIndex property controls that ability for the Tab to move in that order.
We shall set the TabIndex property of the toolbox controls accordingly.
For operations that involve two numbers such as calculating the sum, difference and the like: we want it to be: first number → operation → second number → calculate
For operations that involve only one number such as calculating the reciprocal, square root and the like: we want to disable the second TextBox so that the user would not enter a second number.

Graphical User Interface (GUI) Design: TabIndex Property

The TabIndex property contains a number that represents that order in which the toolbox controls are added to the form.
It determines the order in each toolbox control receives focus when the user presses the Tab key or uses an Access key while an application is running.
The TabIndex property is zero-indexed. This means that the first one begins with a 0, the next one is a 1, the next is a 2 among others.
The TabIndex can be changed by:
(1.) Click the form: → View menu → the Tab Order or
(2.) Click each control and change the TabIndex property from the Properties menu.
It is important to note that some toolbox controls do not have a TabIndex property.

Form1.cs: Adjust and Align
(Name) property: Leave as is. Do not change
Text property: Scientific Calculator © 2021 SamDom4Peace Designs (Sample)
BackColor property: Web: Olive
ForeColor property: Web: White
Font: property: Font: Times New Roman;     Font Style: Regular;     Size: 18
FormBorderStyle property: Fixed3D
MaximizeBox property: False

We set the MaximizeBox property to False because we do not want the user to maximize the application.
We want the interface to have a consistent look.

The items in the ComboBox are written that way for teaching purposes.
Reviewing those items, it is easy for you to see the operations that involve one number (first number only) and the operations that involve two numbers (the first number and the second number)

Select the first label (click) and TextBox (CTRL) Copy (CTRL + C) and Paste (CTRL + V) Label: Adjust and Align	Text: Second Number:
Select the first label (click) and TextBox (CTRL) Copy (CTRL + C) and Paste (CTRL + V) TextBox: Adjust and Align	(Name): SecondNumberTextBox
Select the first label (click) and TextBox (CTRL) Copy (CTRL + C) and Paste (CTRL + V) Label: Adjust and Align	Text: Result:
Label: Adjust and Align	AutoSize: False (do this first) Text: Delete label5 (Name): ResultLabel BackColor: Web: White BorderStyle: Fixed3D ForeColor: Web: Black
Button: Adjust and Align	Text: Clear &All (Access key: A) (Name): ClearAllButton BackColor: Web: White ForeColor: Web: Black
Copy and Paste Button: Adjust and Align	Text: Clear &Some (Access key: S) (Name): ClearSomeButton
Copy and Paste Button: Adjust and Align	Text: &Calculate (Access key: C) (Name): CalculateButton
Copy and Paste Button: Adjust and Align	Text: E&xit (Access key: x) (Name): ExitButton
Select the four buttons and Format: Make Same Size: Both

Let us make sure the Tab controls are set in order based on the TabIndex Property




The user may decide to use the access key to do the calculation.
However, we want the user to be able to use only the Tab key and perform operations because the some users may not remember access keys. Besides, any two programmers may decide to use different access keys for the same button.
If the user does ALT + C, it leads to the Calculate button and the calculation is done.
Alternatively, the user can decide to move the Tab key to the Calculate button and then press the ENTER key when the focus is on the button. The calculation will also be done.
Either way is fine. However, the use of only the Tab key has the priority.
It is necessary to accommodate users by allowing users to perform operations with Tab keys especially when they do not know the access keys.
Hence, the TabIndex property is important.
Because we would like the tab to move to the Clear All button before the Exit button, let us change the TabIndex properties of the Clear All button and the Exit button.
Click the View → Tab Order again to remove the tab positions.
Click the Clear All button and change the TabIndex property from $11$ to $10$
Click the Exit button and change the TabIndex property from $10$ to $11$
Verify by viewing the tab order again.


Recap:
Assume the user is working with only the keyboard (software design to accommodate users who cannot use the mouse)

(1.) When the user runs the application, the cursor focus should be in the first TextBox waiting for user input.
The user enters a number and presses the tab key

(2.) The next focus should be the ComboBox waiting for the user to make a selection.
The user selects an operation.
If the operation involves only one number, the second TextBox is disabled so the focus moves to the Calculate button.
The command used to disable the TextBox is: TextBox.Enabled = false;
As you can see, to disable a TextBox; the Enabled property of the Textbox is set to the Boolean value: false
If the operation involves two numbers, the cursor focus moves to the second TextBox waiting for the user to enter the second number. The user enters the second number and presses the tab key.
The next focus would be the Calculate button.
The user presses the ENTER key and the calculation is done. The result is displayed in the label: ResultLabel.

(3.) The user presses the tab key and the focus should be the Clear Some button.
The user presses the ENTER key and the entries in the TextBoxes and the label are cleared.

(4.) The user presses the tab key and the focus should be the Clear All button.
The user presses the ENTER key and all entries (all items in the ComboBox) are cleared.

(5.) The user presses the tab key and the focus is the EXit button.
The user presses the ENTER key and the application is closed.

The ComboBox

A ComboBox is a combination of a TextBox and a ListBox.
(https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.combobox?view=net-5.0)
It enables the user to select items from the a list or enter a new value.
It is an object of the ComboBox class.
There are several properties of the ComboBox.
We shall discuss only one property in this module: the SelectedIndex property.
The SelectedIndex property gets or sets the index of a selected item.
The ComboBox items are zero-indexed just like arrays.
This means that the first item has index: $0$, the second item has index $1$, and the third item has index $2$ among others.
The command used to specify a selected item in the ComboBox is: ComboBox.SelectedIndex == Index
Based on the items in the ComboBox in our program:

Code our Program (Write the Program Code)

(1.) Double-click the Calculate button in the Design window.
This leads to the Code window
Scroll a little bit to the top, write the comments, and begin to...

(2.) Write the code.
What should happen when the user clicks the Calculate button?
Please review the screenshots.
Review the comments.

Design Area
Access keys: C for the Calculate, A for the Clear All, S for the Clear Some and x for the Exit buttons


Program Code
Another approach to clearing texts in the Textbox is to use the Clear() method. For example: Textbox.Clear();
To clear all the items in a ComboBox besides the selected item, we also use the Clear() method. For example: ComboBox.Items.Clear();
To clear the selected item in a ComboBox, we use the command: ComboBox.ResetText();
















Student: Mr. C, you used the same name variable: result for different events.
Is that allowed?
Teacher: Very good observation.
Yes, we can do that.
Here is the reason: we used it within each event (each conditional statement).
We defined it as a class member variable. But remember we did not specify any value for it.
Hence, we are free to use it as local variables.
But you are very welcome to use different variables for the different events if you choose.
Notice that we did not have issues with the variables we defined in the class such as firstNumber
We can use those variables anywhere within the class.
Student: Another question.
You did not convert the variable: result back to a string. It is a double...right?
I thought we were supposed to convert it back to a string to display it in the label because the label accepts only strings just like the TextBox. Is that correct?
Teacher: That is correct.
We are supposed to convert it back to a string in order to display it in the label.
However, the String Interpolation takes care of that.
That is one of the several benefits of using String Interpolation in the formatting of the output.
Notice I have been using it since we discussed it in Module 1
Student: I guess those whitespaces are to format the display of the result?
Teacher: That is correct.

Run the Program

Some Substantive Posts

(1.) Visit my website on Numbers
(www.numbersandnotations.appspot.com/numbers.html)
Choose any applicable question and write a C# program to solve it.
Please make sure that the output of your program gives the same result as the solution of the question on my website.
You may use Arithmetic Operators, Math Functions, or both.

(2.) Visit my website on Percent Applications
(www.fractions-decimals-percents.appspot.com/percentApplications.html)
Choose any applicable question and write a C# program to solve it.
Please make sure that the output of your program gives the same result as the solution of the question on my website.
You may use Arithmetic Operators, Math Functions, or both.

(3.) Program to determine your age
***Because your age is a PII (Personal Identifiable Information), you may use a fictitious age. However, you need to test it (privately) with your actual age to make sure it works.***
Develop a C# program to determine your age based on these instructions.
ONLY one variable is required.
(Hint: If only one variable is required, this implies that you need to use Compound Assignment operators)
The user wants you to note that these instructions would only work for ages determined this year, and wants you to specify it in the program.
(a.) Pick an integer between $0$ and $10$ ($0$ and $10$ exclusive).
(b.) Multiply the integer by two.
(c.) Add five to the result.
(d.) Multiply the result by fifty.
(e.) If you already had your birthday this year, add the result to one thousand, seven hundred and seventy-two. If you have not had your birthday this year, add the result to one thousand, seven hundred and seventy-one. (valid for 2022, adjust accordingly after 2022)
(f.) Subtract your four-digit birth year from the result.
Run the code and display the output.
Explain your result.

(4.) A client wants you to develop a program to calculate the age of his child.
The instructions for the previous question still applies to this question.
However, in this case; the program will give the instructions to the child, and the child will respond.
This program is an Input/Output program.
Develop a C# program for this child.

(5.) Program to determine your date of birth.
***Because your date of birth is a PII (Personal Identifiable Information), you may use a fictitious age. However, you need to test it (privately) with your actual age to make sure it works. Develop a C# program to determine your date of birth based on these instructions.***
ONLY one variable is required.
(Hint: If only one variable is required, this implies that you need to use Compound Assignment operators).
(a.) Pick the integer that is your month of birth.
(b.) Multiply the integer by two hundred.
(c.) Add three hundred and eighty two to the result.
(d.) Divide the result by two.
(e.) Add your day of birth to the result.
(f.) Multiply the result by 100.
(g.) Add thirteen thousand, eight hundred and forty to the result.
(h.) Add the last two digits of your year of birth to the result.
(i.) Subtract thirty two thousand, nine hundred and forty from the result.
Run the code and display the output.
Explain your result.

(6.) A client wants you to develop a program to calculate the date of birth of her child.
The instruction for the previous question still applies to this question.
However, in this case; the program will give the instructions to the child, and the child will respond.
This program is an Input/Output program.
Develop a C# program for this child.

(7.) Develop a Body Mass Index (BMI) desktop application using the United States System.
Test each condition just like we did in our example for the United States System.
Address user-input errors.

(8.) Develop a Body Mass Index (BMI) console application using the International System.
The formula is on the screenshot.
Test each condition just like we did in our example for the United States System.
Address user-input errors.

(9.) Develop a Body Mass Index (BMI) desktop application using the International System.
The formula is on the screenshot.
Test each condition just like we did for the United States System.
Address user-input errors.

Questions (10.) and (11.) are meant to prepare you for the Midterm Project.
For Questions (10.) and (11.)
Develop a C# program that meets these requirements.
(I.) Consider any concept/scenario that uses conditional statements.
It will be great if you find a real-world application. However, you can make up your own.
If you decide to make up your own, please explain the scenario and the conditions well.
If you use a real-world application, please cite your source(s) accordingly. Explain the scenario and the conditions well.
Use at least two (two or more) different conditions.
The BMI Calculator has four different conditions.
But, please use any application that has at least two different conditions.
(II.) Accept user input(s).
(III.) Address user input errors.
(IV.) Test your program and display the result/output for each condition.
(V.) Test your program for user-input errors.
(VI.) Submit all the screenshots accordingly.

(10.) Develop a console application for your concept.

(11.) Develop a desktop application for your concept.

Textbook Questions
(12.) Question (6.) (needs Question 5) on Page 97

(13.) Question (8.) (needs Question 7) on Page 97

(14.) Question (12.) (needs Question 11) on Page 97

(15.) Question (14.) on Page 97

(16.) Question (16.) on Page 98

(17.) Question (2.) on Page 130

(18.) Question (4.) on Page 130

(19.) Question (6.) on Page 130

C# Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) C# Basic Declarations and Expressions : Exercises, Practice, Solution
(B.) C# Basic Algorithm: Exercises, Practice, Solution
(C.) C# Data Types : Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(20.) Please focus only on Questions that deals with Numbers and Operators.
Write the Question as a comment in your program. Include the Title and the Question Number.
Write clear comments for each line of code in the Solution.
Run the program.

For those who do not mind messing around with several languages at the same time
Student: Excuse me, Mr. C
This course is only for C#
What do you mean?
Teacher: You are correct.
But, these subsequent questions are not for everyone.
That is the reason I am putting them at the end.
I have a question for you.
Have you ever seen any IT/Computer Science position that requires the knowledge of only one programming language?
Student: I have not checked, Sir.
Teacher: If you intend to be in the IT/Programming field for the long run, at least four (four or more) languages are required.
If you look for IT positions at Indeed.com or other career/job websites, you will realize what I mean.
Search for c# programmer, you might be surprised that even for entry level positions for a C# Programmer; they require you to have a working knowledge of several other programming languages.
Mr. C is preparing you for that...if you intend to work in the programming field for a long time.
Besides, this is a critical thinking approach.
I am required to develop and promote critical thinking questions for my students.
A programmer is basically a problem-solver irrespective of the programming language used to solve the problem.
Yes, we are working with C#. However, if you find out that Java would be better in solving a particular problem in your workplace, then you need to use Java unless your employer says otherwise.
The knowledge of several languages is a good asset. It makes you highly valuable.
Further, anyone who attempts any of the subsequent questions will still have to write the program in C# and get the same result.
The questions and solutions are in another language.
But the student will have to write the program in C# and come up with the same solution. So, we are still on track.
It is critical thinking...multiple approaches to solving a question.
Be it as it may, these subsequent questions are not required.
It is okay even if you do not look at them. 😊

Java Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) Java Math: Exercises, Practice, Solution
(B.) Java Basic Programming - Part 1: Exercises, Practice, Solution
(C.) Java Basic Programming - Part 2: Exercises, Practice, Solution
(D.) Java Data Types: Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(21.) Please focus only on Questions that deals with Numbers and Operators.
Write the Question as a comment in your program. Include the Title and the Question Number.
Write the program in C#
Run the program. Please make sure your porgram output is the same solution

C++ Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) C++ Basic: Exercises, Practice, Solution
(B.) C++ Basic Algorithm: Exercises, Practice, Solution
(C.) C++ Math: Exercises, Practice, Solution
(D.) C++ Numbers: Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(22.) Please focus only on Questions that deals with Numbers and Operators.
Write the Question as a comment in your program. Include the Title and the Question Number.
Write the program in C#
Run the program. Please make sure your program output is the same solution

Some Substantive Responses

(1.) Provide any of these if it is lacking in any DB post that solved any question in the Assess tab of this module: Well-written comments; another approach/method to solving the question; any additional relevant details; etc.

For Questions (3.) and (4.) in the Substantive Posts
Student: Mr. C, the instructions in Questions (3.) and (4.) are not correct.
The result is not my age.
How can you ask us to write a program that does not work?

(2.) Explain the result to the Student. (Answer this question only if any of your colleagues made a similar statement in the initial post.)

(3.) The Student wants only his/her age to be the result.
Without modifying any of the instructions (but using all of them) and one more instruction, extend the program to display only the Student's age.
What is the extra instruction that you would include to work for all ages? Write it. Run it.

For Questions (5.) and (6.) in the Substantive Posts
Student: Mr. C, I want the date of birth to display properly.
Teacher: Use a delimiter.
Student: What is a delimiter?
Teacher: A delimiter is a sequence of chararcters that specifies limits/boundaries of characters in a text, expression, word, etc.
A good example is the forward slash that you can use to separate that DOB in the form of: mm/dd/yyyy.
The forward slash is a delimiter.
Another example is the pipe delimiter: mm | dd | yyyy.
Another example is the hyphen delimiter: mm-dd-yyyy.
Student: Okay, how do I display the result in that format?

(4.) Explain how you would display the result for the Student.
Write the code. Run it.

(5.) Review the post (Discuss Questions and Assess Questions) done by your colleagues.
If your colleague developed a console application for a program, develop a desktop application for the same program.
If your colleague developed a desktop application for a program, develop a console application for the same program.

(6.) Other substantive responses.

Check Your Understanding

This is the desktop application of the Standard Calculator

(1.) Please review the Functionalities of the Calculator and the Limitations of the Calculator as explained in the Learn tab.
Maintain all the functionalities of the calculator.
Address any or all the limitations.
Submit some clear screenshots that maintains the functionalities.
Submit clear screenshots that addressed the limitations.
You may use my code if you wish (in this case because you are extending the functionalities of my program) and/or your code.

(2.) The first standard calculator we programmed did not contain all the functions.
This is what we did.


This is what you should do.

Develop a calculator that contains all the functions enclosed with a red border besides the plus-minus button: $+/-$
In other words, the plus-minus button is not required.
However, all other functions enclosed within the red border are required.

Please note:
The C function is the Clear function. It deletes everything.
It clears the first number, operation, and the second number.

The CE function is the Clear Entries function. It deletes "some" things.
It clears only the second number. You can replace the second number and continue with the calculation.
It does not clear everything.
This is used when the entire calculation does not need to be deleted.

The BS (backspace) function (you may use alt+174 key if you prefer) is the backspace function.
It deletes part of the first number or the second number.
This is also used when the entire calculation does not need to be deleted.

Let us look at an example. You may test it.

$ \underline{Example} \\[3ex] 25 + 32 \\[3ex] \color{red}{C} \;\; deletes\;\;everything \\[3ex] \color{red}{CE} \;\; deletes\;\;only\;\;32 \\[3ex] \color{red}{BS} \;\; deletes\;\;only\;\;2 \\[3ex] $ This is the desktop application of the Scientific Calculator

(3.) We developed the scientific calculator.
However, it does not contain all the functions.
Develop the scientific calculator GUI that contains all the functions.
You may extend my application by adding the missing functions if you wish, or you may develop your own with all the functions.
You may use my code if you wish (in this case because you are extending the functionalities of my program) and/or your code.

(4.) Develop a console application for an extension of the Body Mass Index (BMI) application example.
We did the application for the United States System (Customary System).
Extend the application by developing the calculator for the International System (Metric System).
The formula is on the screenshot.
Ask the user which system he/she wants to use to calculate the BMI.
Based on the user's selection, display the appropriate output.
Test all the conditions for both systems.

This is the desktop application of the BMI Calculator

(5.) Develop a desktop application for an extension of the Body Mass Index (BMI) application example.
We did the application for the United States System (Customary System).
Extend the application by including the calculator for the International System (Metric System).
The formula is on the screenshot.
Ask the user which system he/she wants to use to calculate the BMI.
Your desktop application should have the dropdown list for both systems, but should be null be default (using a ComboBox)
Alternatively, you may choose to use Radio Buttons.
Based on the user's selection, display the appropriate units for the weight and the height, as well as the output.
Test all the conditions for both systems.
Address user-input errors.

Question (6.) is meant to prepare you for the Midterm Project.
Develop a C# program that meets these requirements.
(I.) Consider any concept/scenario that uses conditional statements.
A real-world application is required. You may not make up your own.
Please cite your source(s) accordingly. Explain the scenario and the conditions well.
Use at least two (two or more) different conditions.
The BMI Calculator has four different conditions.
But, please use any application that has at least two different conditions.
(II.) Accept user input(s).
(III.) Address user input errors.
(IV.) Test your program and display the result/output for each condition.
(V.) Test your program for user-input errors.
(VI.) Submit all the screenshots accordingly.

(6.) Develop a console application and a desktop application for your concept.

Vocabulary Words

character, string, Boolean, bool, concatenator operator, string concatenation, string interpolation, string literal, empty string, date, time, function, method, argument, escape sequences, dot member access operator,

Objectives

Students will:

(1.) Discuss the C# string data type.
(2.) Discuss the C# Boolean data type.
(3.) Discuss Date and Time in C#.
(4.) Write programs that involves the String data type.
(5.) Write programs that involves the Boolean data type.
(6.) Write programs that involves Date and Time.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) Strings (C# Programming Guide) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/)

(3.) System.String Class in .NET (VB and C#) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/api/system.string?view=net-5.0)
Scroll down till you see Methods

(4.) How to (C#) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/how-to/)
Scroll down till you see Working with strings

(5.) DateTime Struct by Microsoft
(https://docs.microsoft.com/en-us/dotnet/api/system.datetime?view=net-5.0)
Scroll down till you see Methods

(6.) Dates, Times, and Time Zones by Microsoft
(https://docs.microsoft.com/en-us/dotnet/standard/datetime/)
Focus on TimeZoneInfo and DateTimeOffset only (not TimeZone)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(7.) Type C# Strings and/or C# Booleans and/or C# Date and Time in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(8.) Type C# Strings and/or C# Booleans and/or C# Date and Time in the search bar and view/read the results.

Required Readings

Strings

A String is a sequence of ordered characters.
It is built out of characters.
It is enclosed in matching double quotation marks.

Remember the first C# program we wrote, the output...the message, THANK GOD.
That is an example of a string.
Let us review more examples of what we could do with C# strings.

Join Strings (Concatenate Strings)
Let us discuss several ways of joining strings (or concatenating strings).
Concatenate means to join or link together.
String concatenation is the joining of strings.
Please review the screenshots and the comments.

First Approach: String Concatenation using the Concatenator operator
The concatenator operator is the plus sign: +


Second Approach: String Interpolation
This uses the special character, $ (dollar sign), double quotes, and braces.
The braces are optional. However, they are required if the values of variables are to be included.
The variables are enclosed in braces.


Third Approach: String.Concat Method
This method is one of the .NET (C# and VB) system methods.
It concatenates two or three specified instances of String.
This implies that it can accept two or three arguments.
It will concatenate two strings if you enter two strings as the arguments.
It will concatenate three strings is you enter three strings as the arguments.


Fourth Approach: String.Join Method
This method is one of the Visual Basic methods. But it can be used for C# also.
It concatenates as many strings as you want.
This implies that it can accept several string arguments.
Notice the format of the fullName variable in the code


Student: Mr. C, must we use variables with all these approaches?
Teacher: Not at all.
You can use the strings directly rather than using variables.
In that case, for the String Interpolation; you would not need the braces.

String Escape Sequences

String Escape Sequences are used to turn special characters into strings.
Sometimes, we write sentences that has the single quotation marks and the double quotation marks.
How do we display such sentences in a C# program?
We have to use the backslash escape sequence
There are several escape sequences. Please see the List of String Escape Sequences
Also, check out: Escape Sequences
In this module, we shall focus on the use of the Backslash escape sequence.
As we make progress, we may use some more escape sequences.
Let us demonstrate the use of the backslash escape sequence in inserting single quotes, double quotes, and backslash in sentences.

Insert single quote, double quote, backslash in sentences

Booleans

Teacher: What are you looking at?
You already know.
Student tries to hide it.
Teacher: I want to ask you something.
Look at it.
Please turn it off...remember the course syllabus.
Before you turn it off, do you see two numbers in the Power off button?
Student: Numbers?
I do not see numbers.
It's an icon.
Teacher: Yes, they are numbers.
The numbers are: $0$ and $1$
$1$ is inside the $0$ in most devices.
Student: Interesting.
Teacher: $0$ represents OFF
$1$ represents ON
You see these two numbers in almost all electronic devices (tablets, smartphones, computers) including some electric switches.
In Logic, $0$ represents FALSE
$1$ represents TRUE
We use true and false Boolean values in Statements including conditional statements and iterative statements. We shall cover Statements in the next module.
The use of these two numbers: $0$ and $1$ in Mathematics and Computer Science to repesent FALSE and TRUE values is known as Boolean Algebra
It was developed by George Boole, an English mathematician/philospher/logician.
We can also use these Boolean numbers $0$ and $1$ to represent choices/options of NO and YES


A Boolean is a fundamental data type in C# that:

(1.) is declared with the keyword, bool or Boolean
However, it is recommended to use the bool keyword.
The bool keyword represents the Boolean data type.

(2.) can represent only one of two states: True or False

(3.) gives an output of only one of two values: True or False

(4.) is used for comparison (in relational/comparison operators) to compare expressions.

(5.) is used in statements (conditional statements and iterative statements) to make decisions.

A Boolean Expression is an expression that returns a Boolean value.
Let us demonstrate some examples of the use of Booleans.

Booleans: Example 1




Booleans: Example 2



Student: Mr. C, why is it better to use the bool keyword?
The Boolean keyword has the same functionality. Right?
Teacher: That is correct.
However, the bool keyword is used to denote the Boolean data type
Just as the string keyword is used to denote the String data type
Just as the int keyword is used to denote the Integer data type

Date and Time

Date and time stamps are needed for: transactions, receipts, appointments, agreements, events, rules/laws, and tickets (by cops and troopers) among others.
Besides, we shall use the date and time functions in the midterm project.

Notable Notes on C# Date and Time
(1.) Date is a data type (Value Type) in .NET standard (C# and VB) declared as DateTime

(2.) You can also use the var keyword (variable) to declare it.
We shall be using the var keyword as applicable.

(3.) It covers the date and time range from: 0:00:00 (midnight) on January 1, 0001 through 11:59:59 PM on December 31, 9999

(4.) It is an object of the DateTime Structure.

(5.) It has several constructors, properties, methods, and operators.

If you did not understand Numbers (4.) and (5.), do not worry.
I shall explain more in the comments in the screenshots.

(6.) For all arithmetic operations (especially Addition and Subtraction operations) involving Date and Time, please use only the built-in operators.
This is important to avoid getting errors (especially errors of undercounting or overcounting by 1, 0.1, 0.001)
The built-in operators are: .Add, .Subtract, etc.
Do not use the "usual" arithmetic operators.

This is what I mean.
For example: to determine the number of days of the sum of two dates:
Do: example1.Date.Add(example2.Date).Days;
Do Not: (example1.Date + example2.Date).Days;

For example: to determine the number of days of the difference between two dates:
Do: example1.Date.Subtract(example2.Date).Days;
Do Not: (example1.Date - example2.Date).Days;

Before we continue, let us review the format specifiers for displaying date and time in .NET (C# and VB)

My Preferred Approach
I think this is the easiest approach.
(1.) Declare a String variable for the Full date/time pattern (long time)
For example: string currentDateTime = DateTime.Now;

(2.) To get only the date; use the code: currentDateTime.ToLongDateString();
(3.) To get only the time; use the code: currentDateTime.ToLongTimeString();

Or if you really like writing short codes (short form):
(1.) string currentDate = DateTime.Now.ToLongDateString();

(2.) string currentTime = DateTime.Now.ToLongTimeString();

Alternatively:
(1.) Begin by using the Full date/time pattern (long time)
Declare a DateTime variable to store the current date and time using the Full date/time pattern (long time)
For example: DateTime currentDateTime = DateTime.Now;
(2.) To get only the date; use the code within a String Interpolation: currentDateTime.ToLongDateString();
(3.) To get only the time; use the code within a String Interpolation: currentDateTime.ToLongTimeString();
Please see the implementation of this approach in the screenshots for the Birthday Application.
There are several date/time format methods that you can use with that variable.
Just type the variable and press the dot access member operator (the decimal point button on your keyboard) and start reviewing the list of methods you can use.
You can also press the dot access member operator and press "T" (ToString methods) so you can see more methods.
Have fun exploring 😊

There are several approaches to handling dates and times in C#
Let us discuss some of them.

As at today: 03/01/2021; Kent State University has 8 Ohio campuses, several other U.S campsuses, and four campuses outside the United States otherwise known as Kent State Worldwide.
Kent State Worldwide consists of Kent State in Florence, Italy; Geneva, Switzerland; New Delhi, India; and Beijing, China.
Mr. C wants to greet all his students in the United States and Worldwide.
He wants to great them in their local dates and times.
He would kindly ask you, his student (please check out one of the Questions in the Assess tab) to teach him the greeting in your language.
But his work right now is to display the Full date/time pattern (long time) of each country: United States, Italy, Switzerland, India, and China.
Because we shall be working with foreigh countries, it is necessary to include: using System.Globalization namespace
To get the current local date and time (date and time according to the user's computer system), the syntax is:
DateTime currentDateTime = DateTime.Now;

To get the local date and time of the user (say in the United States), the syntax is:
var dateTimeUSA = currentDateTime.ToString("F", CultureInfo.CreateSpecificCulture("en-US"));
where:
USA is the country (you can replace with your country)
dateTimeUSA is the variable name (you can use any appropriate name you prefer)
"F" is the format specifier for the Full date/time pattern (long time) (you can use any format specifier you like)
CultureInfo.CreateSpecificCulture("en-US") is the System command/code for displaying the full date and time in United States English language.
The specific culture is en-US
en is English Language
US is the United States
Just as: CultureInfo.CreateSpecificCulture("es-MX") is the code to display the full date and time in Mexican Spanish Language.
The specific culture is es-MX
es is Spanish Language
MX is Mexico

So, the command follows the syntax:
CultureInfo.CreateSpecificCulture("specific culture")

This is the List of Countries, Languages, and Specific Culture for Displaying Date and Time
(https://www.samdomforpeace.com/References/ASCII.html#specificCulture)

But, there is an issue.
The issue is displaying the current times in other countries.
The specific culture works for displaying the dates and times in the languages (several languages) of different countries as applicable
However, we still need to display the actual times (not the local user's time) for any country as applicable
Moreover, depending on the time of the day in each country, the dates might be incorrect as well.
In other words, we want to greet each Kent State University student according to his/her country's time/time zone (not according to my time/time zone)
We want to display the current date and time of each country that has Kent State University campus.
So, we need the time zone names and IDs of different countries

As at today: 03/05/2021 the time zone names and IDs of several countries in .NET are:
Names and IDs of Time Zones for Different Countries









Note that these time zone IDs should be entered as strings.
If a country is not listed, then we will need to find the UTC (Universal Time Coordinated) and the offset as applicable.
Then, we look up any country with the same UTC and offset that is listed, and use that country.
How?
Bing or Google "time zone for country and look for the UTC time zone of the country that is mot listed.
If it is UTC+4, then find an applicable country that has UTC+04:00 and use that country.
Alternatively, contact Microsoft and ask them to include your country/city/county/province/region.

Say we want to display the current date and time in Mexico City, we look up the time zone name and ID:
Guadalajara, Mexico City, Monterrey => Central Standard Time (Mexico)
We convert the local user's date and time (local user is in the United State) using the code:
var dateTimeMEX = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(currentDateTime, destinationTimeZoneId: "Central Standard Time (Mexico)")

Then, we use the specific culture to get the date and time in Mexican Spanish
var dateTimeMexico = dateTimeMEX.ToString("F", CultureInfo.CreateSpecificCulture("es-MX"))

Please review the screenshots and the comments.

Date and Time: Example 1: Current Date and Time in Different Countries




Student: What if we want to display the date and time in several states across the United States?
Our students come from all 50 states of the United States as well as the United States territories.
And you know there are different time zones in the United States.
How do we display the current date and time in those states in their respective time zones?
Teacher: Very good question.
In that case, we have to get the current date and time of the user
DateTime currentDateTime = DateTime.Now;

Then, we use the specific culture of each state to get the current date and time in that state.
For example; say we want the current date and time in the State of Ohio
The specific culture for the State of Ohio is en-OH
The code will then be:
DateTime dateTimeOhio = currentDateTime.ToString("F", CultureInfo.CreateSpecificCulture("en-OH"));

This is the List of the States and Territories of the United States for Displaying Date and Time
(https://www.samdomforpeace.com/References/ASCII.html#specificCultureUS)

Student: So, we do not use the TimeZoneInfo class like we did for foreign countries?
Teacher: We do not.
Because it is the U.S.A 😊
But, we can if we want to. We just have to find the appropriate destination ID
But it is much simpler to just use the specific culture for the date and time for the states and territories of the United States.

Let's develop another date and time function application.
What are some of your memorable events? dates for those events?
Student: Birthday, Christmas...I'm always looking forward to it
Teacher: Let's write a program in that regard.
I shall use my birthday as an example.
Let us calculate how many days there are until my birthday.
We shall begin with a console application.
Then we shall develop a desktop application and explore more toolbox controls.
An interesting toolbox control to explore is the Timer.
Have you noticed those websites where you see a Timer that displays a countdown of the times: days and hours:minutes:seconds to a particular event?
Student: Yes, I have.
Teacher: Cool. So, we shall explore that control and some other controls for the GUI.
As at today: 03/02/2021, my birthday is yet to occur. However, it is important to add a functionality to the program to display a message to the user if the user's birthday has already occurred prior to today.
Student: I guess we shall ask the user to enter the birthday?
Teacher: Yes. Let's use an Input/Output feature to make it interactive.
The program will ask the user to enter the birth year, birth month, and birth day.
If the birthday has occurred, inform the user accordingly. Then, display a positive message informing the user that we look forward to his/her next "age" birthday.
If the birthday is yet to occur, display the number of days remaining until the birthday.
If the user's birthday is today, we shall greet the user with a HAPPY BIRTHDAY greeting.
This will require a conditional statement.
Student: You know Mr. C, we have been using Statements since Module 3 when we are supposed to cover it in Module 5.
Teacher: That is correct. It goes to show how important they are in programming.
It is okay to introduce you to them so you get familiar with using them.
We shall cover them in detail in Module 5. It is a broad topic.
Please review the screenshots and the comments.

Date and Time: Example 2: Birthday Application

GUI Programming: Birthday Application

MonthCalendar, Button, RichTextBox, Label, and Timer

Let us develop a desktop application of the Birthday app.
We are gradually learning these toolbox controls as we make progress in the course.
We shall work with two additional controls in this section: the MonthCalendar control and the Timer control

The MonthCalendar Control allows us to select a date from a calendar.
(https://docs.microsoft.com/en-us/dotnet/desktop/winforms/controls/monthcalendar-control-windows-forms?view=netframeworkdesktop-4.8)
According to Microsoft: the Windows Forms MonthCalendar control presents an intuitive graphical interface for users to view and set date information.
The control displays a grid containing the numbered days of the month, arranged in columns underneath the days of the week.
You can select a different month by clicking the arrow buttons on either side of the month caption.

The additional control we shall use is the Timer control.
The Timer Control is a control that determines how an application responds after a certain amount of time passes.
(https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/controls/control-timer)
It is an object of the Timer Class
(https://docs.microsoft.com/en-us/dotnet/api/system.timers.timer?view=net-5.0)

Please review the desktop applications we developed in previous modules.

Design User Interface and Set Properties

Form1.cs: Adjust and Align
(Name) property: Leave as is. Do not change
Text property: Birthday App © 2021 SamDom4Peace Designs (Sample)
BackColor property: Web: Cyan
Font: property: Font: Times New Roman;     Font Style: Regular;     Size: 18
FormBorderStyle property: Fixed3D
MaximizeBox property: False

The MaximizeBox property is set to False if we do not want the user to maximize the application.
The reason is because we want the interface to have a consistent look.

Design Area
Access keys: B for the Birthday Mesage button and x for the Exit button

Code our Program (Write the Program Code)

When the form loads, we do not want to see the label that has the timer
When the user's birthday is today, we do not want to see the label that has the timer.
When the user already had his/her birthday this year, we do not want to see the label that has the timer.
When the user is yet to have his/her birthday this year, we want to see how many days, how many hours, how many minutes, and how many seconds until the user's birthday this year.

(1.) Double-click any empty space on the form in the Design window.
This leads to the Code window
Scroll a little bit to the top, write the comments, and begin to...

(2.) Write the code.
Let us use a top-down approach.
Double-click each button in the Design window to open the Code window.
Then write the code for the event: what should happen when the user clicks the button?
Please review the screenshots.
Review the comments.

Program Code










Run the Program






Student: I have several questions.
Teacher: Please go ahead.
Student: Line #159 in the code: \t, what is it?
Teacher: It is an escape sequence that represents a horizontal tab space
Student: The second result: which is correct: 109 days until your birthday versus 108 days, 6 hours, 34 minutes, and 51 seconds?
Teacher: What do you think?
Which one is more accurate?
Student: The second one I guess.
Teacher: Yes, the second one is more accurate.
The first one is rounded (an estimate)
If you do a quick seearch on Bing or Google for: how many days until Christmas, you will see the first one


The second one is accurate.




Those are the results from two different websites.
Student: My next question deals with the same Line #159 in the code
I guess that goes back to the second question.
Teacher: That is correct.
Using time.days (time from the Timespan data type) is more accurate that using daysBirthday (days from the difference of the DateTime data type variables)
Student: The next question: You basically used the same code you wrote for the Button_click event for the Timer_Tick event?
Is there not a way to reuse codes without having to copy and paste each time?
Teacher: Very good observation and very good question.
I did it because we are yet to cover Functions
Of course, one of the advantages of functions (both system-defined functions and user-defined functions) is for code reusability.
I would have used a user-defined function for the application had we covered Functions before now.

Required Substantive Posts

You may use strings not written in English language. However, if you use any language other than English language, please make sure you translate it. Your colleagues and I need to understand any language you use.
Insensitive words or any word deemed inappropriate to any race, gender, religion, and national origin among others are unacceptable. Any violation will not yield any point.
If you are not sure of the words/string to use, please contact me first.

Remember DB 3 Requirement. There are enough functions for everyone. If all the functions are done, please attempt another question.

.NET (VB and C#) String Methods: Part 1 (Examples are written in C#) Less work
Please review the: System.String Class in .NET (VB and C#) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/api/system.string?view=net-5.0)
Scroll down till you see Methods

(1.) Pick any four methods besides the ones I discussed
Write the code examples for each method and implement each of them.
Run your codes.
Display the results.

VB String Methods: Part 2 (Examples are written in VB) A little extra work because you need to write in C#
Please review the: String Functions in Visual Basic
(https://docs.microsoft.com/en-us/dotnet/visual-basic/language-reference/functions/string-functions)

(2.) Pick any four methods besides the ones I discussed
Write the code examples for each method and implement each of them.
Run your codes.
Display the results.

DateTime Structure
Please review the: DateTime Struct by Microsoft
(https://docs.microsoft.com/en-us/dotnet/api/system.datetime?view=net-5.0)
Scroll down till you see Methods

(3.) Pick any four methods besides the ones I discussed
Write the code examples for each method and implement each of them.
Run your codes.
Display the results.

(4.) Please review the Date and Time example in this module.
Our students come from the entire 50 states of the United States and its territories.
However, the United States has different time zones.
Find out/browse/learn/discover the different time zones in the United States and its territories as seen in the The Official U.S. Time (https://time.gov/) according to the National Institute of Standards and Technology
Include those time zones in your comments.
Display the current date and time for each time zone.
Verify your answer with the times and time zones on that website.

C# Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) C# Strings : Exercises, Practice, Solution
(B.) C# Date and Time: Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(5.) Write the Question as a comment in your program. Include the Title and the Question Number.
Write clear comments for each line of code in the Solution.
Run the program.

For those who do not mind messing around with several languages at the same time
Student: Excuse me, Mr. C
This course is only for C#
What do you mean?
Teacher: You are correct.
But, these subsequent questions are not for everyone.
That is the reason I am putting them at the end.
I have a question for you.
Have you ever seen any IT/Computer Science position that requires the knowledge of only one programming language?
Student: I have not checked, Sir.
Teacher: If you intend to be in the IT/Programming field for the long run, at least four (four or more) languages are required.
If you look for IT positions at Indeed.com or other career/job websites, you will realize what I mean.
Search for c# programmer, you might be surprised that even for entry level positions for a C# Programmer; they require you to have a working knowledge of several other programming languages.
Mr. C is preparing you for that...if you intend to work in the programming field for a long time.
Besides, this is a critical thinking approach.
I am required to develop and promote critical thinking questions for my students.
A programmer is basically a problem-solver irrespective of the programming language used to solve the problem.
Yes, we are working with C#. However, if you find out that Java would be better in solving a particular problem in your workplace, then you need to use Java unless your employer says otherwise.
The knowledge of several languages is a good asset. It makes you highly valuable.
Further, anyone who attempts any of the subsequent questions will still have to write the program in C# and get the same result.
The questions and solutions are in another language.
But the student will have to write the program in C# and come up with the same solution. So, we are still on track.
It is critical thinking...multiple approaches to solving a question.
Be it as it may, these subsequent questions are not required.
It is okay even if you do not look at them. 😊

Java Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) Java Strings: Exercises, Practice, Solution
(B.) Java Date and Time: Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(6.) Write the Question as a comment in your program. Include the Title and the Question Number.
Write the program in C#
Run the program. Please make sure your program output is the same solution

C++ Programming Exercises, Practice, Solution by W3Resource
Please review:
(A.) C++ Strings: Exercises, Practice, Solution
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(7.) Write the Question as a comment in your program. Include the Title and the Question Number.
Write the program in C#
Run the program. Please make sure your program output is the same solution

Required Substantive Responses

(1.) Review the post (Discuss Questions) done by your colleagues.
Use a different string method to work on the same string used by your colleague.

(2.) Review the post (Discuss Questions and Assess Questions) done by your colleagues.
If your colleague developed a console application for a program, develop a desktop application for the same program.
If your colleague developed a desktop application for a program, develop a console application for the same program.

(3.) Other substantive responses.

Check Your Understanding

You may use strings not written in English language. However, if you use any language other than English language, please make sure you translate it. Your colleagues and I need to understand any language you use.
Insensitive words or any word deemed inappropriate to any race, gender, religion, and national origin among others are unacceptable. Any violation will not yield any point.
If you are not sure of the words/string to use, please contact me first.

We are yet to do Statements (in the next Module), but you can give this question a try.
A string palindrome is a word, phrase, clause or sequence of characters that is spelled and read the same way backward and forward.
In other words, when one reads it as is, reverses it and reads it again; the pronunciation is the same.
Examples include the:
Words: HANNAH, BOB, madam, level, civic, racecar, rotor
Phrase: never odd or even
Clause: nurses run
Sentence: Was it a car or a cat I saw?

(1.) Write a C# program that asks for user input.
Determine if the user input is a string.
If the user input is not a string, ask the user to enter only a string.
If the user input is a string, determine if it is a string palindrome.
Inform the user whether it a string palindrome or not.
Test at least one example of: Words, Phrase, Clause, and Sentence that was listed.
This implies that you should test at least four examples.

(2.) Please review the Date and Time: Example 1: Current Date and Time in Different Countries
Extend my application by greeting your fellow colleagues in the langauge of their countries.
Because Visual Studio did not display the Hindi and Chinese alphabets, do not worry about India and China.
Write a C# application that:

(a.) Displays the current date and time for the countries: United States, Italy, and Switzerland.
Because you are extending my application, you may use my code.
Find out/browse/learn/discover the greetings for Good Morning, Good Afternoon, and Good Evening for Italy and Switzerland in Italian and German respectively.

(b.) Displays the greetings to each user (your fellow colleague) according to their countries (the current times in their countries).

If the time is between 12:00:01 AM to 12:00:00 PM (inclusive), greet Good Morning in each langauge.
If the time is between 12:00:01 PM to 04:00:00 PM (inclusive), greet Good Afternoon in each lanaguage.
If the time is between 04:00:01 PM to 12:00:00 PM (inclusive), greet Good Evening in each language.
You may use 12-hour or 24-hour time formats.
These are the minimum requirements. You are welcome to add more functionalities.

(3.) Please review the Date and Time example in this module.
Our students come from the entire 50 states of the United States and its territories.
However, the United States has different time zones.
Find out/browse/learn/discover the different time zones in the United States and its territories as seen in the The Official U.S. Time (https://time.gov/) according to the National Institute of Standards and Technology
Include those time zones in your comments.
Display the current date and time for each time zone.
Greet each user (your fellow colleague) according to their time zones (their own current times).
If the time is between 12:00:01 AM to 12:00:00 PM (inclusive), greet Good Morning.
If the time is between 12:00:01 PM to 04:00:00 PM (inclusive), greet Good Afternoon.
If the time is between 04:00:01 PM to 12:00:00 PM (inclusive), greet Good Evening.
You may use 12-hour or 24-hour time formats.
These are the minimum requirements. You are welcome to add more functionalities.

(4.) Please review the Date and Time: Example 2: Birthday Application
Modify my application or write your new application.
(a.) Ask the user to also enter the time (hh:mm:ss) in hours, minutes, and seconds that he/she was born.
(b.) If the user has not had birthday this year, inform the user about the number of days, hours, minutes, and seconds until his/her birthday.
Do not stress about the calculations. Microsoft.NET methods handle most of these calculations.
(c.) If the user already had birthday this year, or if today is the user's birthday; display appropriate positive messages to the user.
(d.) A user's birthday is 29th February. This implies that the user has to celebrate birthdays only on leap years (years that are divisble by 4). Accommodate that user in your application. Display message(s) accordingly.
(e.) Include checks for user-input errors and display messages accordingly.

(5.) Write a C# program that solves Question (8.) on the Applications of Numbers website.
(https://numbersandnotations.appspot.com/numbersApplications.html)
Use any actual date that is a Tuesday.
Ensure that the output of your program corresponds to the solution on the website.
Please display: the actual date, the actual day, the new date and the new day in your output.
In other words, I am looking for the input date that corresponds to a Tuesday, the input day that is the Tuesday, the output date that corresponds to a Friday, and the output day that is the Friday.
Please check to ensure your program gives the correct output (result).
You may develop a console application or a desktop application for this program.
Submit screenshots of the question, your program, and the output of your program.

(6.) Please review the GUI Programming: Birthday Application
We developed the Birthday desktop application using the MonthCalendar control.
Another option is to use the DateTimePicker Control
(https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.datetimepicker?view=net-5.0)
The DateTimePicker control allows the user to select a date and a time and to display the date and time with a specified format.
The advantage of the DateTimePicker control over the MonthCalendar control is the ability of the user to select only a date and a time.
The advantage of the MonthCalendar control over the DateTimePicker is that it allows the user to select only dates (one date or a range of dates) without selecting time.
In the comments for that program: Lines #48 and #49, I ask that you extend the application.
Develop a desktop application that meets these requirements.
(a.) Ask the user to also enter the time (hh:mm:ss) in hours, minutes, and seconds that he/she was born.
You may use the DateTimePicker control or any other toolbox control you prefer.
(b.) If the user has not had birthday this year, inform the user about the number of days, hours, minutes, and seconds until his/her birthday.
Do not stress about the calculations. Microsoft.NET methods handle most of these calculations.
(c.) If the user already had birthday this year, or if today is the user's birthday; display appropriate positive messages to the user.
(d.) A user's birthday is 29th February. This implies that the user has to celebrate birthdays only on leap years (years that are divisble by 4). Accommodate that user in your application. Display message(s) accordingly.
(e.) Include checks for user-input errors and display messages accordingly.

(7.) Develop a traffic light desktop application using C#
(a.) You may use the Panel toolbox control (https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.panel?view=net-5.0) and/or your own appropriate pictures with the PictureBox toolbox control (https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.picturebox?view=net-5.0) for the lights: Green, Yellow, and Red.
(b.) Set the timer for the duration of the yellow light to be at least two seconds (two seconds or more) before it turns to red.
(c.) Use any appropriate time durations for the green light and the yellow light.
(d.) You are welcome to add more functionalities.

(8.)

Vocabulary Words

statement, flow control, flow of execution, statement block, nested blocks, declaration statements, expression, expression statements, control flow statememts, selection statements: if, else, swich, case; iteration statements: do, for, foreach, in, while; jump statements: break, continue, default, goto, return, yield; exception handling statements: throw, try-catch, try-finally, try-catch-finally; checked and unchecked statements, await statement, yield return statement, fixed statement, lock statement, labeled statements, empty statement, top-level statements, using statement, conditional statements, decision-making statements, decisions, looping statements, loops, repetitive statements, branching statements, branches,

Objectives

Students will:

(1.) Discuss Statements in C# programming language.
(2.) Write selection statements.
(3.) Write iteration statements.
(4.) Write jump statements.
(5.) Write some exception handling statements.
(6.) Write programs that solve real-world problems using statements.
(7.) Complete the Midterm Project on Piecewise Functions.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) Statements (C# Programming Guide) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/statements-expressions-operators/statements)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(3.) Type C# Statements in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(4.) Type C# Statements in the search bar and view/read the results.

(5.) Top-level Statements by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/tutorials/exploration/top-level-statements)

(6.) using statement (C# Reference) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement)

Required Readings

Statements

A statement is an individual instruction of a program.
It ends with a semicolon.
It forms a complete unit of execution.
It is equivalent to a sentence in a language.
It can consist of a single line of code (single-line statement).
It can also consist of multiple lines of code (multi-line statements) in a block, known as a statement block.
A statement block is enclosed in curly braces {} and can contain nested blocks.
A block is a group of zero or more statements between balanced curly braces that can be used where a single statement is allowed.
In Example 3 (If-else statement) as seen in the screenshot below; the if statement is the first block of code and the else statement is the second block of code.
The order in which statements are executed in a program is called the flow of control otherwise known as flow of execution.
The flow of control varies every time a program is run.
It depends on how the program reacts to the instruction it receives at run-time.

There are several types of statements in C#
We have discussed some of them in previous modules.
We shall discuss some of them in this module.
We shall discuss some of them in subsequent modules.
As at today: 03/12/2021; the statements in C# are:

(1.) Declaration Statement
A declaration statement declares a variable or constant.
To declare a variable, the data type must be specified as well. You have the option of assigning a value to it.
To declare a constant, the keyword must be specified. A value must be assigned to it.
// Declaration statement
// We started using this statement beginning from Module 2
int num1 = 7;


(2.) Expression Statement or Expression
An expression statement or an expression is a construct made up of variables, operators, and method invocations, which are constructed according to the syntax of the language, that evaluates to a single value.
Expression statements calculate a value must store the value in a variable.
// Expression statement
// We covered this statement in Module 3
double result = 7 * (5 - 2);


Control Flow Statements
Generally, statements in C# are executed from top to bottom, in the order that they appear.
However, control flow statements control the order in which statements are executed.
In other words, they break up the flow of the execution of statements by using decision making, looping, and branching; thereby allowing a program to execute particular blocks of code conditionally.
They include:

(3.) Selection Statements or Conditional statements or Decison-making Statements or Decisions
A selection statement allows the user to branch to different code sections depending on one or more conditions.
They are the: if statement, if-else statement, if-then statement, if-then-else statement, Multiple ifs statement, and the switch statement.

(4.) Iteration Statements or Looping Statements or Loops
An iteration statement allows the user to perform the same set of statements repeatedly until a specified condition is met.
It also allows the user to loop through collections such as arrays.
They are the: for loop, foreach loop, while loop, and the do-while loop statements.

(5.) Jump Statements or Branching Statements or Branches
A jump statement allows the user to transfer control to another section of the code.
They are the: break statement, continue statement, goto statement, return statement, and the default statement.

Let us discuss the Selection, Iteration, and Jump statements.
Then, we can discuss more statements.

Selection Statements

(1.) If statement
This statement is used when there is only one condition.
If some condition is met, execute a given task.
The If statement is written as:

                            if (condition) 
                            { 
                                statement;
                            }
                    

C# ignores whitespaces so you can also write it this way:

if (condition) { statement; }

(2.) If-else statement
This statement is used when there are only two conditions.
If first condition is met, execute a given task.
else execute another task.
The else refers to the other condition.
Please note that we do not specify the condition for the else statement because we already know it is the other (remaining) condition.
The If-else statement is written as:

                        if (condition) 
                        {
                            statement;
                        } 
                        else 
                        {
                            statement;
                        } 
                        

C# ignores whitespaces so you can also write it this way:

if (condition) { statement; } else { statement; }

We can also write simple If-else statement using the Ternary operator
It can be used for simple if-else statements.
The syntax is:

                        variable = if (condition) ? statement if true : statement if false;
                    

(3.) If-else if-else statement
This statement is used when there are more than two conditions in which the first condition is used for the If statement, other conditions are used for the else if statements, and the last condition is used for the else statement.
Please note that the last condition for the else statement is not specifid in the code because it is the remaining condition.
It is generally known as the remaining condition after all other conditions are specified.
Assume we have only four conditions for a particular program:
The If-else if-else statement is written as:

                        if (condition 1) {
                            statement;
                        } else if (condition 2){
                            statement;
                        } else if (condition 3) {
                            statement;
                        } else {
                            statement;
                        } 
                    

Whitespaces are ignored in C#. Therefore you can also write it this way:

                        if (condition 1) { statement; } 
                        else if (condition 2) { statement; } 
                        else if (condition 3) { statement; } 
                        else {statement; }
                    

Keep in mind that we do not specify condition 4 in the code for the else statement because we already know that the else statement would only be executed if all the other prior conditions are not met.

(4.) Multiple Ifs statement
This statement is used when there are more than two conditions in which each condition is uniquely different.
You can also use this statement if you are not comfortable using the If-else if - else statement.
Both statements accomplish the same task.
Assume we have only four conditions for a particular program:
The Multiple Ifs statement is written as:

                            if (condition 1) {
                                statement;
                            }
                            if (condition 2){
                                statement;
                            }
                            if (condition 3) {
                                statement;
                            }
                            if (condition 4) {
                                statement;
                            } 
                    

Whitespaces are ignored in C#. Therefore you can also write it this way:

                            if (condition 1) { statement; } 
                            if (condition 2) { statement; } 
                            if (condition 3) { statement; } 
                            if (condition 4) { statement; }
                    

Review the Definitions of Numbers
(www.numbersandnotations.appspot.com/#definitions)
Selection Statements: Example 1 (If statement)



Student: What if the user enters $5$?
Teacher: Very good question.
What do you think?
Student: I'm not sure.
But, I'm guessing it will not run.
Teacher: The program will still run.
However, there will be no output.
Do you know the reason?
Student: Because there was no condition in the If statement to check for that?
Teacher: That is correct.
We did not specify what should happen if num1 is 0 or if num1 is greater than 0.
We need to specify all conditions.
Let's check it out

Selection Statements: Example 2 (If statement is NOT enough for this example)



Teacher: As we can see, it did not display any output.
How do we take care of this?
Student: Include the condition in the conditional statement
Teacher: I know. 😊
How do we include it?
Let us see what we can do.

Selection Statements: Example 3 (If-else statement)




Student: But, Mr. C; what if I do not want to use the If-else statement?
What if I decide to use Multiple Ifs statements for that same example?
Will it not work?
Teacher: It will work.
You can use Multiple Ifs statements if you know you will cover all the conditions.
It will give the same output as the If-else statement.
Let us try it.

Selection Statements: Example 4 (Multiple Ifs statements)





Teacher: Let us rewrite Example 3 using the Ternary operator
The Ternary operator is the short hand approach of writing an if-else statement.

Selection Statements: Example 5 (If-else statement using the Ternary operator)





Let us look at more examples.
Recall: In English Language, Finite Mathematics, Discrete Mathematics; some of the ways to join simple statements to make a compound statement are:
(I.) Use of the conjunction, and which is denoted by && in C#
(II.) Use of the disjunction, or which is denoted by || in C#

Let us review an example where we shall use the conjunction, and

Conditional Statements: Example 6 (If-else statement and the use of the conjunction, and (&&))





Student: What if we have a set of numbers and we want to see if those numbers are positive odd numbers?
Teacher: Great question.
That brings us to an array or list of numbers.
The use of arrays and loops is a more efficient approach of solving those kinds of questions.
We shall cover arrays in another module.
However, we can still do something here.
We shall use two variables to capture two user-input values.
Let us try it with two numbers.

Conditional Statements: Example 7 (Multiple If-else statements, use of "and" (&&))



Student: What if the user enters a decimal?
Teacher: Good question.
What do you think?
Student: Mr. C...
The teacher that answers questions with questions
Teacher: It is a teaching technique. 😊 I do that sometimes but not all the time
So, what do you think?
Student: I feel it will not work
Teacher: That is correct.
The program will not run
It will not execute, not to mention give an output.
Instead, the IDE compiler will throw an exception because we defined the user input as an integer data type rather than as a double data type.
It is one of the mechanisms of Exception Handling.
Student: What is Exception Handling?
Teacher: It is the response to exceptions during run time (when a computer program runs).
Student: What are exceptions?
Teacher: In simple terms, exceptions are errors such as user-input errors, file system errors, and division by zero among others.
We've been handling user-input errors...remember the BMI application we did in Module 3?
We did not call it an exception because we are yet to cover the topic of Exception Handling.
We shall cover some of it in this Module and the rest of it in the Advanced C# course.
Let us discuss a real-world application of selection statements that will lead us to your Midterm project.

Piecewise Functions

A good application of C# Selection Statements is seen in Piecewise functions.
Please review the Story on Piecewise Functions
(www.piecewise-functions.appspot.com/#story)
Let us write several C# programs that will solve the Piecewise function problem in that story.

Piecewise Function: Selection Statements using Multiple Ifs statements
Selection Statements: Example 8 (Multiple conditions: Multiple ifs)





Let us address user-input errors for the number of burritos that may be out of range in the Piecewise Function.
It is important to address user-input errors in any program you write.
In this case (for the Story on Piecewise Functions): the program will not display any output if the user enters a negative number, a zero, or any positive number greater than the upper bound of the last piece.
The user may then be confused if he/she does not see any output.
We want to avoid that.
In the case of user-input error, we want the program to display a message that the user entered something out of range, and then exit without interrupting the system.
Hence, we wrote the message for the user and included the Environment.Exit(0); method to exit the program.

What if the user enters $2500$?


What if the user enters $-3$?


Student: Can we write the same Piecewise function using the If-else if-else statements?
Teacher: Nice question.
What do you think?
Student: I think we can.
Teacher: Yes but we need to include the last else statement
Student: Must we include it?
Teacher: Highly recommended...yes
However, the program will work even if we do not include it.
But my recommendation is that whenever you use if-else statement, make sure you include the last else statement
In this case (using the if-else if-else statement), the last elsestatement will have a statement but not a condition.
It is executed when all prior conditions are not met.
So, let us write a statement that will display the message to the user if the user enters any value that is out of range. using the If-else if-else statements

Piecewise Function: Selection Statements using If-else if-else statements
Selection Statements: Example 9 (Multiple conditions: If-else if-else statements)





What if the user enters $0$?


What if the user enters $3000$?


What if the user enters $-12$?


Teacher: Did you notice the importance of that final else statement?
We did not need to specify the range of numbers that are out of bounds as we did for the Multiple-Ifs statements.
In other words, we do not specify the condition for the else statement.
Also, it is better to inform the user what he/she entered.
Typically, the user is supposed to notice it after the message we wrote for the Multiple-Ifs
However, it is better to show the user what was entered, as well as the message.

(5.) Switch statement
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/switch)
Another selection statement is the switch statement. It is an alternative to an if-else statement if a single expression is tested against three or more conditions.
The switch statement is a selection statement that selects a single switch section to execute from a list of cases based on a pattern match with the match expression.
It includes one or more switch sections. However, it chooses only one section.
Each switch section contains one or more case labels followed by one or more statements.
The case labels consists of a case and/or the default label.
At most one default label may be placed in any swtich section of a switch statement.

The match expression in a switch statement can be any non-null expression.
It is a variable of these data types: character; string; bool; integral values such as integer, long; and enumeration types.
No two case labels may contain the same expression (variable).

C# does not allow the execution of statements from one switch section to the next switch section.
In that regard, each switch section must be exited by using a jump statement such as the break, goto, or return statement. The break statement is normally used.

Which selection statement should you use? If-else or Switch statement?
The option to use if-then-else statements or a switch statement depends on the readability and the expression that the statement is testing.
An if-then-else statement can test expressions based on ranges of values or conditions, while a switch statement tests expressions based only on a single integer, enumerated value, or String object.

The general syntax of the switch statement for the Integer data types (Byte, Short, and Integer data types) is:

                            variable 
                            switch (variable)
                            {
                            case 1: 
                            	statement;
                            	break;
                            case 2:
                            	statement;
                            	break;
                            case 3:
                            	statement;
                            	break;
                            default:
                            	statement;
                            }
                        

Case 1
The switch block compares the value of the variable with 1
If the value of the variable is 1, then it executes the statement in case 1 and breaks, thus ending the program.
If the value of the variable is not 1, it moves on to case 2 and compares the value of the variable with 2
If the value of the variable is 2, it executes the statement in case 2, breaks, and ends the program.
Otherwise, it moves to case 3.
It compares the value of the variable with 3
If that value is 3, it executes the statement in case 3 and breaks. The program ends.
If that value is not 3, it executes the statement in the default
As noted, the break statement ends the program when the value of the variable is equal to the case number, otherwise the switch statement moves on to the next case and continues the comparison.

Teacher: Have you noticed these Call Center greetings?
For English, press 1; Para Español, marque dos.
Student: Yes I have.
You mean to say: For Spanish, press 2.
Teacher: Yes.
Let us write a simple application for that greeting using a simple Select-Case statement.
We can add more simple features..."spice it up".

Switch Statements: Example 1: Call Center Greetings






Let us review more examples of the switch statement

Let us write a Switch statement that involves the use of the String data type.
Rather than asking for user-input, we can also initialize the variable.
Remember, we can use any of the variables we listed previously.





But, I really prefer the user-input feature. It makes for an interactive application.
Let us modify the application to accept user input.
In that case, we do not initialize the String variable.








Please answer these questions.
Review the last two slides of the output.

Question $1$
(1.) Explain why the slide with the user-input of $52$ displayed that output.

Question $2$
(2.) The user entered "africa" and expected to see the statement associated with that continent.
However, the user saw another output.
Explain.

Recall the Piecewise Function program we wrote earlier.
We used Conditional statements to write it.
Let us develop the same program using the Switch statement.
We shall use the Switch statement and the Ternary operator to write the program.

Piecewise Function Application using the Switch Statement and the Ternary Operator

Nested Conditional Statements

                           dataType variable;
                            if condition 1
                            {
                                If condition 2
                                { 
                                    statement;
                                }
                                else
                                { 
                                    statement;
                                }
                            } 
                                 
                            else if condition 3
                            { 
                                if condition 4
                                {
                                    statement;
                                } 
                                else
                                { 
                                    statement;
                                }
                            } 
                            
                            else
                            { 
                                statement; 
                            } 
                        

Iteration Statements

Iteration Statements repeat a group of statements a specified number of times.

They are the:
(1.) For Loop
(2.) While Loop
(3.) Do-While Loop
(4.) Foreach Loop

(1.) For Loop statement
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/for)
The for iteration statement executes a statement or a block of statements while a specified Boolean expression evaluates to true.
The general syntax of a for loop is:

                            for (initializer; condition; iterator)
                            {
                        	    statement;
                            }
                        

This is also written as:

                            for (variable = beginValue; condition; variable compound_assignment someValue)
                            {
                        	    statement;
                            }
                        

where the:
for keyword begins the For loop. It is required.
initializer is the beginning value of the variable. It can be optional.
condition is the condition required for the variable to reach the final value. It can be optional.
iterator is the incremental or decremental value for the beginning value of the variable to reach the final value. It can be optional.

Declare a variable and initialize it.
For the variable to satisfy the condition until the final value of the variable, execute the statement.

(2.) While Loop statement
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/while)
The while iteration statement executes a statement or a block of statements while a specified Boolean expression evaluates to true.
It executes zero or more times because that Boolean expression is evaluated before each execution of the loop.
The general syntax of a while loop is:

                            initializer;
                            while (condition)
                            {
                        	    statement;
                        	    iterator;
                            }
                        

This is also written as:

                            variable = beginValue;
                            while (condition)
                            {
                        	    statement;
                        	    variable compound_assignment someValue;
                            }
                        

where the:
while keyword begins the While loop. It is required.
initializer is the beginning value of the variable. It can be optional.
condition is the condition required for the variable to reach the final value. It can be optional.
iterator is the incremental or decremental value for the beginning value of the variable to reach the final value. It can be optional.

Declare a variable and initialize it.
While the condition is being met, execute the statement.

(3.) Do-While Loop statement
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/do)
The do-while iteration statement executes a statement or a block of statements while a specified Boolean expression evaluates to true.
It executes one or more times (unlike the while loop that executes zero or more times) because that expression is evaluated after each execution of the loop.
The general syntax of a do-while loop is:

                            initializer;
                            do 
                            {
                        	    statement;
                        	    iterator;
                            } 
                            while (condition);
                        

This is also written as:

                            variable = beginValue;
                            do 
                            {
                        	    statement;
                        	    variable compound_assignment someValue;
                            } while (condition);
                        

where the:
do keyword begins the Do-While loop. It is required.
initializer is the beginning value of the variable. It can be optional.
condition is the condition required for the variable to reach the final value. It can be optional.
iterator is the incremental or decremental value for the beginning value of the variable to reach the final value. It can be optional.
while keyword ensures that the condition is being met. It is required.

Declare a variable and initialize it.
Do the statement and iterate it while the condition is being met.

Jump statements in action
At any point within the for loop, the while loop, and the do-while loop:
We can break out of the loop by using the break statement
We can step to the next iteration in the loop using the continue statement
We can exit the loop using the goto statement, return statement, or the exception handling statement: throw statement.

(4.) Foreach Loop statement
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/foreach-in)
The foreach iteration statement executes a statement or a block of statements for each element in a collection (array)
The general syntax of a foreach loop is:

                            foreach (var item in collection)
                            {
                                statement;
                            }
                        

We shall implement the foreach statement in Module 7 (Arrays).

We also have infinite while loop: while(true)
It is the while statement used with the Boolean value of true
We use the break statement to break the loop
We shall discuss these kinds of loops later.

Depending on the program, we can nest any statement within any statement as needed.
Let us write some code examples
Please review the screenshots and the comments.

Example 1: Print the even numbers less than $25$
This approach uses the Definition of an even number. It has a nested selection statement (if-statement).
Use three different iteration statements.




Example 2: Another way to print even numbers less than $25$
This approach uses incremental values of $2$. It does not have a nested selection statement (if-statement).
Use three different iteration statements.




Example 3: Print the perfect squares between 1 and 100 (1 and 100 are inclusive)




Student: It seems I do not understand this
Teacher: What do you not understand?
Student: Initializing the variables
Line #15 and Line #16: you initialized num1Squared and num2Squared
Why did you not initilize num3Squared?
Teacher: I can...if I wanted to
However, it is not necessary to do so.
Line #20: I was going to use num1Squared (numSquared < 100)
If I did not initialize it before using it, it will be an error.
The same applies to Line #31 (num2Squared < 100)
But, it does not apply to the do-while loop because in Line #45, it was defined with the formula
We are supposed to define a variable after declaring that variable
After defining it, then we can use it.
But if we decide to use it after declaring it without defining it, there will be an error.
So, it was not necessary for me to initialize num3Squared to 1 because I defined it in Line #45 before using it in Line #49
Student: So, initializing it is seen as defining it?
Teacher: Yes...in that case/sense
Student: Another question
The program prints the perfect squares between $1$ and $100$ (both ends inclusive)
However, the condition in the program for those three different loops used less than 100
Should it not be less than or equal to 100?
Teacher: Very good question
Here's the thing:
If we use less than or equal to 100, it will print $121$ and stop at $121$ rather than 100
The program is executed in a top-down approach
So, the number will increment to 11 and print the square of 11 before the program ends.
This is because 100 is less than or equal to 100
Based on the way we wrote the program, the number increments, then is squared, then the square is printed, and then the condition (whether the square is less than 100)
So, in order to print only that range (1 - 100), we want the program to stop at the condition when the square is less than 100.
If the square is less than or equal to 100, it will continue, and then allow the number to increment to 11, square it to give 121, and the print it before that condition that stops it. We do not want it that way.
Does it make sense?
Student: I don't think so.
Is there another way we can solve this question?
Teacher: Yes of course.
We can nest an if-statement inside the first two iteration statements: (for-loop and while-loop).
In that case, we shall not initialize those variables.
Also, we shall use the less than or equal to 100 in that approach.
Let us write the program using that approach.

Example $4$: Another way to print the perfect squares between 1 and 100 (1 and 100 are inclusive)
This approach uses a nested selection statement (if-statement).
Use three different iteration statements.




Teacher: Is this appraoch better?
Student: Much better.
We also used only two variables.

In Nigeria, we had to recite Multiplication Tables (from 2 * 12 to 12 * 12) in the kindergarten/elementray school
These Multiplication Tables are written on the back of most exercise books.
Input/Output feature: Let us write the Multiplication Table for a number (an integer)
Input: We shall ask the user to enter an integer
Output: The program will print the multiplication table for that integer.

Example $5$: Print the Multiplication Table for a number





We can also use decrement operators
We must not always increment.
For example: let us

Midterm Project

The midterm project is designed to assess your knowledge of Statements in solving real-world problems.
It is a Piecewise Function application.
Any other application will not considered.

Please:
(1.) Visit my website on: Piecewise Functions
(www.piecewise-functions.appspot.com)

(2.) Read the Story to understand the idea of Piecewise functions.

(3.) Read the Overview of Piecewise Functions for more understanding of Piecewise functions.

(4.) Study the Applications of Piecewise Functions

(5.) Review the Project Examples. Ensure you follow all the instructions and directions.

(6.) Review the Midterm Project rubric for your course.

(7.) Complete the Midterm Project for your course.

(8.) Ask questions. I can help.
If you have any issue at any time and you have reviewed the resources I provided and you cannot fix the issue, please attend the Office Hours/Live Sessions so I can help you.

(9.) Include all these: (documentation of all your Math work and the .exe file) in OneDrive, create a shareable link, and post the link in the Midterm Project Drafts forum of the course on Blackboard or send to me via email.
You may also upload them directly if you prefer.
I shall review and provide feedback.

(10.) When you are done with your project:
Make sure your executable file runs by itself outside the project folder
If it does run, include these three items: single executable file (that runs by itself outside the folder), the Math documentation (Word document that has the Math part), and the entire project folder, into a folder, zip the folder (.zip extension only) and submit it in the appropriate area of the Blackboard course.
If it does not run, please fix it.
If you cannot fix it, please attend the Office Hours/Live Sessions so I can help you.

NOTE: Any actual project submitted to me via email will not be graded.

If you wish to save some time for research:
Please review the Piecewise Function projects done by my previous students.
The direct link of the verifiable websites are included.
(I.) VB Projects
(II.) C# Projects
(III.) C++ Projects
(IV.) Java Projects

You may not do any same application done by any of my previous students for C#
You may do any Piecewise Function application not done by any of my previous students for C#.
If you are not sure what project you may or may not do, please contact me via the school email.

Vocabulary Words

method, function, main method, system pre-defined method, user-defined method, common language runtime (CLR), method signature, method name, method parameter, parameter list, method access, access level, public, private, abstract, sealed, return value, return type, void, method invocation, instance method, static method, argument, argument list, pass parameters by value, pass parameters by reference (ref keyword), parameter arrays, extension methods, async methods, expression-bodied members, expression body definitions, iterators, modifier, local variables, return keyword, value parameters, reference parameters, pass parameters by output (out keyword), pass parameters by input (in keyword),

Objectives

Students will:

(1.) Discuss methods.
(2.) Pass parameters to methods (Pass by Value, Pass by Reference).
(3.) Pass arguments to methods (Pass by Position, Pass by Name).
(4.) Overload methods.
(5.) Write programs that solves real-world problems using methods.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) Methods (C# Programming Guide) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/methods)

(3.) Methods in C# by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/methods)

(4.) out parameter modifier by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/out-parameter-modifier)

(5.) in parameter modifier by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/in-parameter-modifier)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(6.) Type C# Methods or C# Functions in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(7.) Type C# Methods or C# Functions in the search bar and view/read the results.

Required Readings

Methods

                        // Method
                        using System;
                    
                        namespace Methods
                        {
                            class Program
                            {
                                // Declare the method: SumNumbers 
                                // Parameters are: num1 and num2
                                public static int SumNumbers(int num1, int num2)
                                {
                                    return num1 + num2;
                                }
                        
                                static void Main(string[] args)
                                {
                                    // Call the method
                                    // Arguments are 5 and 7
                                    SumNumbers(5, 7);
                        
                                    // Print what you called
                                    Console.WriteLine(SumNumbers(5, 7));
                                }
                            }
                        }
                        

Void type Method Example

Celsius Temperature to Fahrenheit Temperature Conversion
Given: The Human Body Temperature in Celsius Temperature ($37^\circ$)
To Calculate: The Fahrenheit Temperature

Formulas:
$ fahrenheitTemp = \dfrac{9 * celsiusTemp}{5} + 32 \\[5ex] $

Data type Method Example

Fahrenheit Temperature to Celsius Temperature Conversion
Given: The Human Body Temperature in Fahrenheit Temperature ($98.6^\circ$)
To Calculate: The Celsius Temperature

$ celsiusTemp = \dfrac{5 * (fahrenheitTemp - 32)}{9} \\[5ex] $

Teacher: Did you notice the difference?
Student: Yes...I think so
I prefer the Void type method
We can easily use the variable names rather than writing the value. I mean ...
I would prefer to use the variable: fahrenheitTemp rather than 98.6
Teacher: I prefer the void method too
It helps if we want to return multiple values along with a message in a String Interpolation
Let us write a code example that uses an Input/Output feature.
We shall also demonstrate the use of local variables.

Void Type Methods Example: Input/Output Feature

Formulas:
$ fahrenheitTemp = \dfrac{9 * celsiusTemp}{5} + 32 \\[5ex] celsiusTemp = \dfrac{5 * (fahrenheitTemp - 32)}{9} \\[5ex] $

Data Type Method Example: Input/Output Feature

Discriminant of a Quadratic Trinomial (no worries, we do not discriminate in Mathematics 😊)
Calculate the Discriminant of a Quadratic Trinomial in General Form

Why Are We Learning Methods?

(1.) Program Requirement
Every line of executable code in any C# application must be inside some method.

(2.) Reusability: write one time, use several times
Methods are useful for performing repeated or shared tasks such as frequently used calculations, text and control manipulations, and database operations.
We can just define a method one time, and then reuse the statements inside the method as many times as we want whenever we call that method.

(3.) Easier Code Readability and Faster Debugging
Imagine a "big" program (program with long lines of codes).
Methods allow such programs to be broken into discrete logical units.
This helps for easier code readability and faster debugging.

(4.) Avoiding Code Duplication
After developing a method in one program, it can be reused in another program with little or no modifcation.

Passing Parameters: By Value or By Reference

There are two ways to pass parameters to a method in C#
They are:
(1.) Pass by Value (Value Parameters)
In the previous examples we did for the Void type and Data type methods; we passed parameters by value because the default passing mechanism is to pass parameters by value.

(2.) Pass by Reference (Reference Parameters)
When we pass parameters by reference, we use the ref keyword before the data type in the parameter variable as well as before its corresponding argument.

As we learned earlier:
When we declare a method, we use parameters.
When we call the method, we use arguments.

In C#, a paramter can be passed to a method by value or by reference
Passing Mechanism is the passing of a parameter to a method by value or by reference.
It determines whether the method can modify the programming element underlying the argument in the calling code.
Please note that passing mechanism is optional in method declarations.
The default passing mechanism in C# (when the passing mechanism is not specified) is to pass parameters by value.

Choice of Passing Mechanism

Definitions:
A local variable is a variable declared within a method.
A member variable is a variable declared inside a class or structure, but not within any method internal to that class or structure.
We shall focus on only local variables in this module.

Student: Mr. C, if I say I did not understand the passing mechanism you just explained, I mean it.
I want to learn and understand it, rather than just memorize.
Is there any way you can break it down?
Teacher: Yes, let's do some examples.
Student: Alright, but please use a simple example.
You have been using Mathematics examples.
Can you explain this time with English...say using Strings?
Teacher: Okay. Not a problem. Let's do the examples.

Pass Parameters by Value: Example $1$


Pass Parameters by Reference: Example $1$


Student: So, when we pass parameters by value, the arguments are printed; and when we pass paramaters by reference, the parameters (rather than the arguments) are printed.
Is that correct?
Teacher: That is correct.
When we pass parameters by value (which is the default passing mechanism when the passing mechanism is not specified), the copies of the parameters (which is the arguments) are printed.
The actual parameters are not affected.
Only the arguments (which are the copies of the parameters) are printed.
When we pass parameters by reference, the actual parameters are affected because the actual parameters become associated with the arguments passed to the function.
Would you like for us to do another example?
Student: Yes please.
But keep it simple.
Teacher: Okay. Let's do an example with numbers.

Pass Parameters by Value: Example $2$


Pass Parameters by Reference: Example $2$


Student: I get it now.
But, what if we decided to print the values in the user-defined method rather than the main method?
Teacher: Then the program will print the parameters in that user-defined method
Student: Regardless of the passing mechanism?
Teacher: Yes...
Provided you did not print anything in the Main Method
So, this is what happens
When the user-defined method is called in the main method, the program will head to the user-defined method and execute every statement there.
So it will print whatever it sees there
And head back to the main method
And if it sees there is no print command in the main method, it will not print anything on the console.

Parameters passed by Reference can further be passed by output or passed by input
Let us discuss them.

Passing Arguments: By Position and By Name

We have seen the two ways we can pass parameters.
Let us discuss the two ways we can pass arguments.
When we call a Method, we can pass the arguments by position or by name
In the examples we did so far, we passed the arguments by position.
Passing Arguments by Position is passing the arguments in the order in which they appear in the method's declaration when we defined the parameters.
It is delimited (separated) by commas
You can omit an argument when you call the method if you made it optional with the corresponding parameter.
However, if you do; it's place must be held with a comma.

Passing Arguments by Name is passing the arguments without regard to position.
They can be passed in any order. However, we must specify the name of the parameter followed by a colon followed by the value of the argument (parameterName: argumentValue)
You can omit an argument when you call the procedure if you made it optional with the corresponding parameter.
But the nice thing about this approach is that you do not have to use commas to denote missing positional arguments.
Another nice feature about this approach is that you do not have to follow the order in which the parameters were defined in the method.
Further, this approach makes it easier to note which arguments you are passing and which ones you are omitting.
Remember when we used this approach... in Module 4 when we covered Date and Time methods
Let us write some code examples.

Pass Arguments by Position Example


Pass Arguments by Name Example

Method Overloading

GUI Programming:

Some Substantive Posts

For all applicable questions, please:
(A.) Use the Void type and/or the Data type as your method
(B.) Use appropriate method names in line with C# naming conventions.
(C.) Include an appropriate message with your result.
(D.) Use an Input/Output feature if you wish.

(1.) Using the Data Type Method Example: Input/Output Feature, include a condition that asks the user if the quadratic trinomial is in general form.
If the user says No, ask the user to arrange the quadratic trinomial in general form before proceeding. Then, quit the program.
If the user says Yes, proceed to run the program.
Test both conditions.

Textbook Questions
(2.) Question 2. on Page 303

(3.) Question 4. on Page 303

(4.) Question 6. on Page 304

(5.) Question 10. on Page 303

Arithmetic: Questions (6.) through (9.)
Please review the Definitions of Numbers on Numbers website: Numbers and Notations
(https://numbersandnotations.appspot.com/#definitions)
Please make sure you indicate the type of number in your comments.

(6.) Write a method that prints any of those types of numbers between one and thirty ($1$ and $30$ are included)

(7.) Write a method that prints the first thirty numbers of any of those types of numbers.
Focus on the first positive thirty numbers of those kind of numbers.

(8.) Write a method that asks the user to input two values (those values could be positive, zero or negative)
The method should print all the numbers for any of those types of numbers between those two values.
Those two values should be included if they are part of those type of numbers.

(9.) Write a method that asks the user to put in a value (that value could be positive, zero, or negative)
The method should print thirty values of those types of numbers up to and including the user-input value.

Geometry: Questions (10.) and (11.)
Please review the Mensuration Formulas on Mensuration website: Mensuration
(https://www.samuelchukwuemeka.com/Mensuration/mensuration.html)
Please make sure you indicate the type of figure/shape in your comments.

(10.) Write a method that asks the user to input the required parameters for any two-dimensional figure.
The method should return the area and perimeter of that figure.

(11.) Write a method that asks the user to input the required parameters for any three-dimensional figure.
The method should return the surface area and volume of that figure.

Strings/Quotes: Questions (12.) and (13.)
Find a quote from any of your favorite authors or your favorite quote.
If you do not have any favorite author or a favorite quote, make up a quote yourself, and indicate that it is your own quote.

(12.) Write a method that prints all the vowels in that quote, and returns the count.

(13.) Write a method that prints all the consonants in that quote, and returns the count.

C# Programming Exercises, Practice, Solution by W3Resource
Please review:
C# Function: Exercises, Practice, Solution
(https://www.w3resource.com/csharp-exercises/function/index.php)
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(14.) Write the Question as a comment in your program. Include the Title and the Question Number.
Write clear comments for each line of code in the Solution.
Run the program.

For those who do not mind messing around with several languages at the same time
Student: Excuse me, Mr. C
This course is only for C#
What do you mean?
Teacher: You are correct.
But, these subsequent questions are not for everyone.
That is the reason I am putting them at the end.
I have a question for you.
Have you ever seen any IT/Computer Science position that requires the knowledge of only one programming language?
Student: I have not checked, Sir.
Teacher: If you intend to be in the IT/Programming field for the long run, at least four (four or more) languages are required.
If you look for IT positions at Indeed.com or other career/job websites, you will realize what I mean.
Search for c# programmer, you might be surprised that even for entry level positions for a C# Programmer; they require you to have a working knowledge of several other programming languages.
Mr. C is preparing you for that...if you intend to work in the programming field for a long time.
Besides, this is a critical thinking approach.
I am required to develop and promote critical thinking questions for my students.
A programmer is basically a problem-solver irrespective of the programming language used to solve the problem.
Yes, we are working with C#. However, if you find out that Java would be better in solving a particular problem in your workplace, then you need to use Java unless your employer says otherwise.
The knowledge of several languages is a good asset. It makes you highly valuable.
Further, anyone who attempts any of the subsequent questions will still have to write the program in C# and get the same result.
The questions and solutions are in another language.
But the student will have to write the program in C# and come up with the same solution. So, we are still on track.
It is critical thinking...multiple approaches to solving a question.
Be it as it may, these subsequent questions are not required.
It is okay even if you do not look at them. 😊

Java Programming Exercises, Practice, Solution by W3Resource
Please review:
Java Methods: Exercises, Practice, Solution
(https://www.w3resource.com/java-exercises/method/index.php)
You are provided with the Questions and the Solutions.
No more than one student may do any specific question.

(15.) Write the Question as a comment in your program. Include the Title and the Question Number.
Write the program in C#
Run the program. Please make sure your program output is the same solution

Some Substantive Responses

(1.) Review the post (Discuss Questions) done by your colleagues.
Use a different statement to work on the same function used by your colleague.
For example: if your colleague used an iteration statement in a function, you may use a conditional statement or a jump statement or a different iteration statement to write the same function to give the same output.

(2.) Review the post (Discuss Questions) done by your colleagues.
Use a different method to display the same output of the program done by your colleague.
For example: if your colleague used the Data type method, use the Void type method to write the program to display the same output.
You may include an appropriate message along with the output.

(3.) Review the post (Discuss Questions and Assess Questions) done by your colleagues.
If your colleague developed a console application for a program, develop a desktop application for the same program.
If your colleague developed a desktop application for a program, develop a console application for the same program.

(4.) Review the post (Discuss Questions) done by your colleagues.
If your colleague used the Void type method to display several values of different data types in an output, use the Passing parameters by Output (out) approach to display the same output.

(5.) Other substantive responses.

Check Your Understanding

Algebra:
Please review the Roots of a Quadratic Equation on the Expressions and Equations website: Quadratic Equations
(www.expressions-equations.appspot.com/#quadraticEquations)
There is a calculator I developed that calculates the roots of a quadratic equation and displays a message.

(1.) Console Application

(2.) Desktop Application

(I.) Write a method that requests the user to input the three values: (as seen on my calculator), and display the same message that is displayed by my calculator.
In other words, the output and message from your calculator should be the same as the output and message from my calculator when the user inputs those three values.
Test your program for each of the four cases of the discriminant regarding the nature of the roots of a quadratic equation as seen in Numbers (1a.), (1b.), (2.) and (3.) on my website.

(II.) Submit clear screenshots of your program.

(III.) Submit clear screenshots of the output of your program for the four cases.

(IV.) Submit clear screenshots of the output of my calculator for the four cases.

(III.) and (IV.) should display the same messages.

(3.)

Vocabulary Words

array, single-dimensional array, one-dimensional array, dimension, rank, data structure, array type, array elements, square brackets, index, array index, array length, sort array, System.Linq namepsace, arrays as parameters, arrays as arguments, array methods, new keyword, object keyword, var keyword, ListBox, MultiLine TextBox, parallel arrays,

Objectives

Students will:

(1.) Discuss arrays.
(2.) Implement some array methods.
(3.) Pass arrays as function parameters.
(4.) Pass arrays as arguments.
(5.) Write programs that use arrays to solve real-world problems.

Recommended Readings and Videos

(1.) Textbook Chapter

(2.) Arrays (C# Programming Guide) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/arrays/)

(3.) Tuple Types (C# Reference) by Microsoft
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-tuples)

Videos:
Please click the RESOURCES tab of this website
Click the LinkedIn Learning (Kent State University) link
Follow the directions to access the website.
(4.) Type C# Array and/or C# Tuple in the search bar and view the results.

Videos and Textbooks:
Please click the RESOURCES tab of this website
Click the O'Reilly Online Learning link
Follow the directions to access the website.
(5.) Type C# Array and/or C# Tuple in the search bar and view/read the results.