STDBOOL.H

this header file contains four macros for a Boolean data type

#define bool _Bool
#define true 1
#define false 0

USAGE

#include <stdbool.h>

bool is_valid = true;

if (is_valid) {
    // do something
}

 * w/o stdbool.h
   int is_valid = 1; // true
   if (is_valid) {
      // do something
   }