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