16. Most useful conditional structures.

  1. If…Then…Else Statement 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.

  1. 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

  1. Select Case

A Select Case statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each select case. Syntax

The syntax for a Select Case statement in VB.Net is as follows − Select [ Case ] expression

  • [ Case expressionlist
    • [ statements ] ]
  • [ Case Else
    • [ elsestatements ] ]

End Select