Option 1:
#include <stdbool.h>
Option 2:
typedef enum { false, true } bool;
Option 3:
typedef int bool;
enum { false, true };
Option 4:
typedef int bool;
#define true 1
#define false 0
Explanation:
Option 1 will work only if you use C99 (or newer) and its the "standard way" to do it.
Choose this if possible
Options 2,3 and 4 will have practice the same identical behavior. #2 and #3 don't use
#defines though which in my opinion is better.