11.1.5 Boolean Type

The unsigned integer type bool holds truth values: its possible values are 0 and 1. Converting any nonzero value to bool results in 1. For example:

bool a = 0;
bool b = 1;
bool c = 4; /* Stores the value 1 in c.  */

Unlike int, bool is not a keyword. It is defined in the header file stdbool.h.