Logical Operators in C: A Comprehensive Guide

Understand the logical operators in C programming that evaluate expressions as True or False. C treats "0" as False and any non-zero value as True, making logical operators essential for decision-making in programs. Learn how to use logical operators efficiently to control the flow of your code.

Logical Operators in C

Logical operators in C evaluate to either True or False and are typically used with Boolean operands. Since C treats "0" as False and any non-zero number as True, any operand to a logical operator is converted to a Boolean value.

Logical Operators

The following table shows the logical operators in C:

Operator	Description	Example
&&	Logical AND operator. If both operands are non-zero, the result is True.	(A && B)
\|\|	Logical OR operator. If any operand is non-zero, the result is True.	(A \|\| B)
!	Logical NOT operator. It negates the logical state of its operand.	!(A)

Truth Tables

Logical AND (&&) Operator

The && operator has the following truth table:

a	b	a && b
True	True	True
True	False	False
False	True	False
False	False	False

Logical OR (||) Operator

The || operator has the following truth table:

a	b	a \|\| b
True	True	True
True	False	True
False	True	True
False	False	False

Logical NOT (!) Operator

The ! operator has the following truth table:

A	!A
True	False
False	True

Examples

Example 1

The following example demonstrates the usage of logical operators in C:

Code


#include <stdio.h>

int main() {
    int a = 5;
    int b = 20;
    
    if (a && b) {
        printf("Line 1 - Condition is true\n");
    }
    
    if (a || b) {
        printf("Line 2 - Condition is true\n");
    }
    
    a = 0;
    b = 10;
    
    if (a && b) {
        printf("Line 3 - Condition is true\n");
    } else {
        printf("Line 3 - Condition is not true\n");
    }
    
    if (!(a && b)) {
        printf("Line 4 - Condition is true\n");
    }
    
    return 0;
}

Output


Line 1 - Condition is true
Line 2 - Condition is true
Line 3 - Condition is not true
Line 4 - Condition is true

Example 2

Logical operators can also work with char types as they are a subset of int:

Code


#include <stdio.h>

int main() {
    char a = 'a';
    char b = '\0'; // Null character
    
    if (a && b) {
        printf("Line 1 - Condition is true\n");
    }
    
    if (a || b) {
        printf("Line 2 - Condition is true\n");
    }
    
    return 0;
}

Output


Line 2 - Condition is true

Example 3

The following example shows a compound Boolean expression in a C program:

Code


#include <stdio.h>

int main() {
    int phy = 50;
    int maths = 60;
    
    if (phy < 50 || maths < 50) {
        printf("Result: Fail");
    } else {
        printf("Result: Pass");
    }
    
    return 0;
}

Output


Result: Pass

Example 4

The same logic can be expressed using the && operator as follows:

Code


#include <stdio.h>

int main() {
    int phy = 50;
    int maths = 60;
    
    if (phy >= 50 && maths >= 50) {
        printf("Result: Pass");
    } else {
        printf("Result: Fail");
    }
    
    return 0;
}

Output


Result: Pass

Example 5

The following code uses the ! operator in a while loop:

Code


#include <stdio.h>

int main() {
    int i = 0;
    
    while (!(i > 5)) {
        printf("i = %d\n", i);
        i++;
    }
    
    return 0;
}

Output


i = 0
i = 1
i = 2
i = 3
i = 4
i = 5

Logical operators are generally used to build compound Boolean expressions and are often used in decision-control and looping statements in C. C also has bitwise counterparts of the logical operators such as bitwise AND (&), bitwise OR (|), and bitwise NOT (~).