Use of bool in C

In C, there is no predefined datatype as bool. However, we can create a boolean type using enum or use the standard <stdbool.h> header (C99 and later). With enum, we create a boolean type where false holds value 0 and true holds value 1.

Syntax

typedef enum { false, true } bool;
// Or using C99 standard
#include <stdbool.h>

Method 1: Using Enum

We can create a custom boolean type using typedef enum −

#include <stdio.h>

typedef enum {
    false, true
} bool;

int main() {
    bool my_bool1, my_bool2;
    
    my_bool1 = false;
    if(my_bool1 == false) {
        printf("my_bool1 is false
");
    } else {
        printf("my_bool1 is true
");
    }
    
    my_bool2 = true;
    if(my_bool2 == false) {
        printf("my_bool2 is false
");
    } else {
        printf("my_bool2 is true
");
    }
    
    printf("false = %d, true = %d
", false, true);
    return 0;
}

my_bool1 is false
my_bool2 is true
false = 0, true = 1

Method 2: Using stdbool.h (C99+)

Modern C provides <stdbool.h> header which defines bool, true, and false −

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

int main() {
    bool is_valid = true;
    bool is_complete = false;
    
    printf("is_valid: %s
", is_valid ? "true" : "false");
    printf("is_complete: %s
", is_complete ? "true" : "false");
    
    /* Boolean operations */
    bool result = is_valid && !is_complete;
    printf("is_valid AND NOT is_complete: %s
", result ? "true" : "false");
    
    return 0;
}

is_valid: true
is_complete: false
is_valid AND NOT is_complete: true

Key Points

• In enum method, false gets value 0 and true gets value 1 automatically.
• The <stdbool.h> approach is standard and preferred in modern C.
• Both methods allow boolean logic operations like &&, ||, and !.

Conclusion

C supports boolean types through custom enum or the standard <stdbool.h> header. The standard approach using <stdbool.h> is recommended for modern C programming as it provides better compatibility and readability.