if then else

An If statement can be followed by an optional Else statement, which executes when the Boolean expression is false.

Syntax:

The syntax of an If...Then... Else statement in VB.Net is as follows:

If(boolean_expression)Then

   'statement(s) will execute if the Boolean expression is true

Else

  'statement(s) will execute if the Boolean expression is false

End If

If the Boolean expression evaluates to true, then the if block of code will be executed, otherwise else block of code will be executed.

Flow Diagram:

VB.Net if...else statement

Example:

Module decisions

   Sub Main()

       'local variable definition '

      Dim a As Integer = 100

      ' check the boolean condition using if statement

      If (a < 20) Then

          ' if condition is true then print the following

          Console.WriteLine("a is less than 20")

      Else

          ' if condition is false then print the following

          Console.WriteLine("a is not less than 20")

      End If

      Console.WriteLine("value of a is : {0}", a)

      Console.ReadLine()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

a is not less than 20

value of a is : 100

The If...Else If...Else Statement

An If statement can be followed by an optional Else if...Else statement, which is very useful to test various conditions using single If...Else If statement.

When using If... Else If... Else statements, there are few points to keep in mind.

An If can have zero or one Else's and it must come after an Else If's.

An If can have zero to many Else If's and they must come before the Else.

Once an Else if succeeds, none of the remaining Else If's or Else's will be tested.

Syntax:

The syntax of an if...else if...else statement in VB.Net is as follows:

If(boolean_expression 1)Then

   ' Executes when the boolean expression 1 is true

ElseIf( boolean_expression 2)Then

   ' Executes when the boolean expression 2 is true

ElseIf( boolean_expression 3)Then

   ' Executes when the boolean expression 3 is true

Else

   ' executes when the none of the above condition is true

End If

Example:

Module decisions

   Sub Main()

      'local variable definition '

      Dim a As Integer = 100

      ' check the boolean condition '

      If (a = 10) Then

          ' if condition is true then print the following '

          Console.WriteLine("Value of a is 10") '

      ElseIf (a = 20) Then

          'if else if condition is true '

          Console.WriteLine("Value of a is 20") '

      ElseIf (a = 30) Then

          'if else if condition is true 

          Console.WriteLine("Value of a is 30")

      Else

          'if none of the conditions is true

          Console.WriteLine("None of the values is matching")

      End If

      Console.WriteLine("Exact value of a is: {0}", a)

      Console.ReadLine()

   End Sub

End Module