Not Operator (!)

A Not operator is represented by an exclamation mark (!). Technically, it’s a unary prefix operator, which means that you use it with one operand, and you code it immediately in front of that operand.

The Not operator reverses the value of a Boolean expression. Thus, if the expression is true, Not changes it to false. If the expression is false, Not changes it to true.

For example:

!(i = 4)

This expression evaluates to true if i is any value other than 4. If i is 4, it evaluates to false. It works by first evaluating the expression (i = 4). Then it reverses the result of that evaluation.

Don’t confuse the Not logical operator (!) with the Not Equal relational operator (!=). Although these operators are sometimes used in similar ways, the Not operator is more general. I could have written the preceding example like this:

i != 4

The result is the same. The Not operator can be applied to any expression that returns a true-false result, however, not just to an equality test.