Guide to Game Development/The Programming Language/VB.NET/If Statement

If statement

An 'if' statement can be used to check the value of a variable and compare it to something else. Here's a list of some comparison/conditional operators:

Conditional Operator	Description
=	Is equal to
<>	Is not equal to
>	Is greater than
<	Is less than
>=	Is greater than or equal to
<=	Is less than or equal to

Example of an if-statement in use

Dim Num1 as Integer = Console.ReadLine()
If Num1 = 5 Then
    Console.WriteLine("They chose the number 5!")
End If

'Stopping the program from closing
Console.ReadLine()

First run of the program

Input:

5

Output:

They have chose the number 5!

Second run of the program

Input:

4

Output:

Example of a greater than being used

Dim Num1 as Integer = Console.ReadLine()
If Num1 > 5 Then
    Console.WriteLine("Their number was greater than 5!")
End If

'Stopping the console from closing
Console.ReadLine()

First run of the program

Input:

8

Output:

Their number was greater than 5!

Second run of the program

Input:

3

Output:

Third run of the program

Input:

5

Output:

Notice that if it was equal to 5, there was no output, to get an output for 5 as well the code could be either changed to > 4 or >= 5

Else

This is to used to active when the if statement isn't true.

Example of Else Statement

Example code:

Dim Num1 as Integer = Console.ReadLine()
If Num1 >= 7 Then
    Console.WriteLine("Their number is greater than or equal to 7.")
Else
    Console.WriteLine("Their number is less than 7.")
End If

First run of the program

Input:

8

Output:

Their number is greater than or equal to 7.

Second run of the program

Input:

7

Output:

Their number is greater than or equal to 7.

Third run of the program

Input:

6

Output:

Their number is less than 7.

Else If

These can be used to check for other things other than the first if statement.

Example of Else If statement

Dim Num1 as Integer = Console.ReadLine()
If Num1 = 8 Then
    Console.Writeline("Equal to 8.")
Else If Num1 >= 7 Then
    Console.WriteLine("7 and more.")
Else
    Console.WriteLine("Everything else (6 or less).")
End If

'Stopping the console from closing
Console.ReadLine()

First run of the program

Input:

9

Output:

7 and more.

Second run of the program

Input:

7

Output:

7 and more.

Third run of the program

Input:

6

Output:

Everything else (6 or less).

Forth run of the program

Input:

8

Output:

Equal to 8.

Notice that the first is accepted, but the second statement is still true, but it didn't run that piece of code, this is because with if statement it goes from top to bottom, when it finds one statement that is true, it doesn't bother checking others.

A way to make both active when they're both true would be to do this:

If Num1 = 8 Then
    Console.Writeline("Equal to 8.")
End If
If Num1 >= 7 Then
    Console.WriteLine("7 and more.")
Else
    Console.WriteLine("Everything else (6 or less).")
End If

Example Input and Output for this new algorithm

Input:

8

Output:

Equal to 8.
7 and more.

You can have many Else If statements in a row

Example:

Dim Num1 as Integer = Console.ReadLine()
If Num1 = 5 Then
    Console.WriteLine("Num1 is 5")
Else If Num1 = 6 Then
    Console.WriteLine("Num1 is 6")
Else If Num1 = 7 Then
    Console.WriteLine("Num1 is 7")
Else If Num1 = 8 Then
    Console.WriteLine("Num1 is 8")
Else
    Console.WriteLine("Num1 isn't 5, 6, 7 or 8")
End IF

'Stopping the console from closing
Console.ReadLine()

Of course this is an inefficient way of coding, a better way would be to write:

Console.WriteLine("Num1 is " & Num1)

However the code above doesn't allow for the else part, for this we'll need to learn about boolean logic operators as seen below.

Boolean Logic Operators

There are 4 main boolean logic operators available: AND, OR and XOR, NOT. Boolean logical operators compare the two boolean statements either side of it and then convert them both into another boolean statement (With the exception of NOT which only affects the boolean statement after it). They are defined as such:

Operator	Description	Truth table
And	Is only true if both the statements are true, else it's false.	Input to the Left Input to the right Output False False False False True False True False False True True True
Or	Is true if either one of the statements are true, or if they are both true. Is only false when both are false.	Input to the Left Input to the right Output False False False False True True True False True True True True
Xor	Is true when either one are true. Is false if they are both true, or if they are both false (Only true if they are different).	Input to the Left Input to the right Output False False False False True True True False True True True False
Not	Inverts the boolean value of the statement that follows it.	Input to the right Output False True True False