Using true and false in C

Question

As far as I can see there are 3 ways to use booleans in c

1. with the bool type, from then using true and false
2. defining using preprocessor #defin

Answer 1

You can test if bool is defined in c99 stdbool.h with

#ifndef __bool_true_false_are_defined || __bool_true_false_are_defined == 0
//typedef or define here
#endif