truthy.c

#include <stdio.h>
#include <stdbool.h>

static void truthy_int(int i) {
  if (i) printf("%d is true\n", i); else printf("%d is false\n", i);
}

int main() {
  truthy_int(-1);
  truthy_int(0);
  truthy_int(1);
  bool t = true;
  bool f = false;
  printf("false = %d\n", f);
  printf("true = %d\n", t);
}