Logical negation operator !

The ! (logical negation) operator determines whether the operand evaluates to 0 (false) or nonzero (true).

C only The expression yields the value 1 (true) if the operand evaluates to 0, and yields the value 0 (false) if the operand evaluates to a nonzero value. C only

C++ only The expression yields the value true if the operand evaluates to false (0), and yields the value false if the operand evaluates to true (nonzero). The operand is implicitly converted to bool, and the type of the result is bool.

The following two expressions are equivalent:

!right;
right == 0;