Boolean Values in C - Sanfoundry

This C Tutorial explains Boolean Values and Whether C have an Explicit Boolean Type.

C doesn’t have an explicit Boolean type so integers are used instead. Boolean values are TRUE and FALSE or ON and OFF or 1 and 0 respectively. According to rule, 1 is considered TRUE and 0 is FALSE. However, any nonzero value is considered to be TRUE and Standard doesn’t say if 1 is more TRUE than any nonzero value. For example, in the following program fragment,

    int a = 10, b = 20;
 
    if (a)
        if (b)
            printf("value of a + b is %d\n", a + b);
 
    /*
     * in this example a and b are integers and used in Boolean context as
     * "if a is TRUE then if b is TRUE then print the value of a + b
     */

Consider another example:

    int a = 10, b = 20;
 
    if (a)              /* if a is nonzero */
        if (b)          /* if b is nonzero */
            if (a == b) /* a & b are being tested as ints not as boolean */
                printf("value of a + b; is %d\n", a + b);

Beware that several nonzero values represent TRUE. In the following program two pair of statements seem to be equivalent. For example:

/*
 * mix_bool_int.c -- program displays ints being tested as boolean values
 */
#include <stdio.h>
#define TRUE 1
#define FALSE 0
 
int main(void) 
{
    int flag;
 
    printf("User, type in some intger value...\n");
    scanf("%d", &flag);
 
    if (flag == FALSE)    /* if flag is zero or false */
        (!flag);          /* set flag to 1 */
 
    if (flag == TRUE)     /* if flag is 1 or true */
         (flag);          /* flag is True */
 
    return 0;
}

But second pair of statements is not equivalent because if flag is given any arbitrary value other than 1, condition won’t hold. This is because of mixing of Integers & Boolean Values. Therefore, the solution to the problem is to avoid using mixed types. And test a given value for zero or nonzero explicitly. For example, in the following program fragment,

    okey = boys_in_class() >= 10;
 
    if (okey)
        printf("Good! We set to work today!\n");
    else 
        printf("See the class on next working day!");

In the above program fragment, the result of relational exp. “boys_in_class() >= 10” is assigned to okey which is then tested for boolean values True and False.

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C99 Standard introduced _Bool Type for Boolean Values. Since boolean values 1 or 0 can be represented by just 1 Bit therefore variable of _Bool Type is 1 bit in memory. For example:

/* bool.c---program displays values of _Bool type */
#include <stdio.h>
#define TRUE 1
#define FALSE 0
 
_Bool new_count();
 
int main(void)
{
    _Bool okey;
    int count = 0;
 
    while ((okey = new_count()) == TRUE) {
        printf("No of Iteration Count is %d\n", ++count);
    }
 
    printf("Bye!\n");
    return 0;
}
 
_Bool new_count()
{
    _Bool new;
    int a, b;
 
    printf("user, enter two intgers...\n");
    scanf("%d %d", &a, &b);
 
    if (a == b)
        return new = 1;
    else
        return new = 0;
}

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