Another handy example is a test to determine if an integer is odd by testing for Number And 1. This will have the value 1 for odd numbers and 0 for even numbers.

Or is 1 (true) if either or both of its arguments are 1 (true). Since it is 1 if either or both of the arguments are 1, it is also called an Inclusive Or, to differentiate it from Xor which we'll discuss next. When used as a mask, a 1 bit in the mask will always create a 1 in the result, but a 0 in the mask will create whatever bit value was in the original. Therefore, Or is usually used as part of a mask to change a selected group of bits to all 1's.

Xor (Exclusive Or) is 1 (true) if either but not both of its arguments are 1. The masking action of Xor is similar to Or since a 0 in the mask will create whatever bit value was in the original. But a 1 in the mask will reverse the value in the original. Xor is usually used to produce the reverse value in a selected group of bits.

Eqv stands for Equivalence, and is 1 (true) if both of its arguments are 1 (true), or if both of its arguments are 0 (false). As an excercise to understanding Eqv, you can see from the table above that:

p Eqv q

is exactly the same as:

Not (p Xor q)

This, in turn, could be written on one line as:

(p Eqv q) Eqv (Not (p Xor q)) == True

Imp (Implies) is perhaps the least used, and least understood, of the logical operators. p Imp q is 1 (true) whenever either p is 0 (false) or q is 1 (true). That is, Imp is False when p is True and q is False (truth cannot imply falsehood) and is True for all other situations (truth can imply truth, and falsehood can imply either truth or falsehood).

The fact that both Eqv and Imp are used very little probably accounts for the fact that they have been dropped from VB .NET. But VB .NET has implemented improved evaluations of And and Or called AndAlso and OrElse. Since logic is logic and doesn't change, the rules we've been talking about here are the same for AndAlso and OrElse. These new operators are only different in the way VB .NET uses the results of the logic. The new operators are discussed in an About Visual Basic article at this link.