What is the _Bool keyword in C?

The keyword _Bool in C is used to represent the built-in boolean data type. _Bool is an unsigned integer type in which 0 represents false and 1 represents true.

Declaration

In C, _Bool can be declared as:

_Bool foo = 0;

OR:

_Bool foo = 1;

Examples

Example 1

Consider the code snippet below, which shows the use of _Bool:

#include<stdio.h>
int main() {
    _Bool foo = 1;
    if(foo){// same as if(foo == 1)
        printf("Boolean is true");
    }else if(!foo){// same as if(foo == 0)
        printf("Boolean is false");
    }
    return 0;
}

Example 2

If _Bool is declared with a value greater than 1, it stores the number as 1:

#include<stdio.h>
int main() {
    _Bool foo = 8;
    if(foo == 1){
        printf("Boolean is true \n");
        printf("Boolean value: %d \n", foo);
    }else if(foo == 0){
        printf("Boolean is false \n");
    }
    return 0;
}

Example 3

When assigned a pointer, _Bool stores 1 if the pointer points to something and stores 0 if the pointer is NULL:

#include<stdio.h>
int main() {
    int a = 10;
    int * ptr = NULL;
    _Bool foo1 = ptr;
    if(foo1 == 1){
        printf("Boolean is true \n");
    }else if(foo1 == 0){
        printf("Boolean is false \n");
    }
    ptr = &a;
    _Bool foo2 = ptr;
    if(foo2 == 1){
        printf("Boolean is true \n");
    }else if(foo2 == 0){
        printf("Boolean is false \n");
    }
    return 0;
}

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