printf("%s", x ? "true" : "false");
// there is no way of pretty-print a boolean with printf
printf("%i", true); // will print 1
printf("%i", false); // will print 0
// but we can create a macro
#define formatBool(b) ((b) ? "true" : "false")
printf("%s", formatBool(true)); // will print true
printf("%s", formatBool(false)); // will print false