<stdbool.h> provides bool, true, and false (C99) as portable names for the _Bool type. Assigning any non-zero value to bool produces 1, unlike int where 42 stays 42.

In C23, bool became a built-in keyword, but including the header remains portable and harmless.

This example shows that bool truncates non-zero values to 1.

// compile: gcc -std=c99 -o stdboolexample stdboolexample.c
// run: ./stdboolexample
// description: bool type behavior with various values
 
#include <stdbool.h>
#include <stdio.h>
 
int main() {
    bool a = 42;
    bool b = -1;
    bool c = 0;
    int d = 42;
 
    printf("bool(42) = %d\n", a);
    printf("bool(-1) = %d\n", b);
    printf("bool(0) = %d\n", c);
    printf("int(42) = %d\n", d);
 
    return 0;
}