Page 70 - C-Language

#define false 0

int main(void) {
bool x = true; /* Equivalent to int x = 1; */
bool y = false; /* Equivalent to int 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!");
}
}

Don't introduce this in new code since the definition of these macros might clash with modern uses
of <stdbool.h>.

Using the Intrinsic (built-in) Type _Bool

C99

Added in the C standard version C99, _Bool is also a native C data type. It is capable of holding
the values 0 (for false) and 1 (for true).

#include <stdio.h>

int main(void) {
_Bool x = 1;
_Bool y = 0;
if(x) /* Equivalent to if (x == 1) */
{
puts("This will print!");
}
if (!y) /* Equivalent to if (y == 0) */
{
puts("This will also print!");
}
}

_Bool is an integer type but has special rules for conversions from other types. The result is
analogous to the usage of other types in if expressions. In the following

_Bool z = X;

• If X has an arithmetic type (is any kind of number), z becomes 0 if X == 0. Otherwise z
becomes 1.
• If X has a pointer type, z becomes 0 if X is a null pointer and 1 otherwise.

To use nicer spellings bool, false and true you need to use <stdbool.h>.

Integers and pointers in Boolean expressions.

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