Page 69 - C-Language

Chapter 8: Boolean

Remarks

To use the predefined type _Bool and the header <stdbool.h>, you must be using the C99/C11
versions of C.

To avoid compiler warnings and possibly errors, you should only use the typedef/define example if
you're using C89 and previous versions of the language.

Examples

Using stdbool.h

C99

Using the system header file stdbool.h allows you to use bool as a Boolean data type. true
evaluates to 1 and false evaluates to 0.

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

int main(void) {
bool x = true; /* equivalent to bool x = 1; */
bool y = false; /* equivalent to bool y = 0; */
if (x) /* Functionally equivalent to if (x != 0) or if (x != false) */
{
puts("This will print!");
}
if (!y) /* Functionally equivalent to if (y == 0) or if (y == false) */
{
puts("This will also print!");
}
}

bool is just a nice spelling for the data type _Bool. It has special rules when numbers or pointers
are converted to it.

Using #define

C of all versions, will effectively treat any integer value other than 0 as true for comparison
operators and the integer value 0 as false. If you don't have _Bool or bool as of C99 available, you
could simulate a Boolean data type in C using #define macros, and you might still find such things
in legacy code.

#include <stdio.h>

#define bool int
#define true 1

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