Visual Basic .NET/Logical operators

Logical Operators

Not

The Not operator returns True when the condition is False. Otherwise, it returns False. Example,

If Not (1 = 2) Then
   MessageBox.Show("(1 = 2) is False. So Not False is True")
End If

Truth Table

Condition	Not Condition
True	False
False	True

And

The And operator returns True when the conditions of the left and right are True. Otherwise, it returns False. Both conditions are evaluated before the result is returned. Example,

If (1 = 1) And (2 = 2) Then
   MessageBox.Show("(1 = 1) is True. (2 = 2) is True. So True And True is True")
End If

Truth Table

Condition1	Condition2	Condition1 And Condition2
True	True	True
True	False	False
False	True	False
False	False	False

AndAlso

The AndAlso operator returns False when the condition on the left hand side is False. Else, it returns True when the conditions of the left and right are True. Otherwise, it returns False. The condition on the right hand side is never evaluated when that on the left hand side is False. This is called short-circuited logic.

Truth Table

Condition1	Condition2	Condition1 AndAlso Condition2
True	True	True
True	False	False
False	-	False

Or

The Or operator returns True when the condition on either side is True. Otherwise, it returns False. Both conditions are evaluated before the result is returned.

Truth Table

Condition1	Condition2	Condition1 Or Condition2
True	True	True
True	False	True
False	True	True
False	False	False

OrElse

The OrElse operator returns True when the condition on the left hand side is True. Else, if the condition on the right hand side is True, it returns True. Otherwise, it returns False. The condition on the right hand side is never evaluated when that on the left hand side is True. This is called short-circuited logic.

Truth Table

Condition1	Condition2	Condition1 OrElse Condition2
True	-	True
False	True	True
False	False	False

Xor

The Xor operator returns True when the condition on the left hand side or right hand side is True, but not when both are True. Xor means "Exclusive OR".

Truth Table

Condition1	Condition2	Condition1 Xor Condition2
True	True	False
True	False	True
False	True	True
False	False	False