What is the C99 _Bool data type and how do you use it?

Include <stdbool.h> header

#include <stdbool.h>

int main(void){
  bool b = false;
}

Macros true and false expand to 1 and 0 respectively.

Section 7.16 Boolean type and values < stdbool.h >

• 1 The header <stdbool.h> defines four macros.
• 2 The macro
  • bool
    expands to _Bool.
• 3 The remaining three macros are suitable for use in #if preprocessing directives. They
  are
  • true : which expands to the integer constant 1,
  • false: which expands to the integer constant 0, and
  • __bool_true_false_are_defined
    which expands to the integer constant 1.
• 4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
  redefine the macros bool, true, and false.