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Home » C programming language

Logical NOT (!) Operator in C

Last Updated : December 17, 2025

Logical operators work with the test conditions and return the result based on the condition's results, these can also be used to validate multiple conditions together.

In C programming language, there are three logical operators Logical AND (&&), Logical OR (||) and Logician NOT (!).

Logical NOT (!) operator in C

Logical NOT is denoted by exclamatory characters (!), it is used to check the opposite result of any given test condition.

If any condition's result is non-zero (true), it returns 0 (false) and if any condition's result is 0(false) it returns 1 (true).

Syntax of Logical NOT operator:

    !(condition)

Truth table of logical NOT operator:

condition	!(condition)
1		0
0		1

C examples of Logical NOT (!) operator

Example 1

Take a number and apply some of the conditions and print the result of expression containing logical NOT operator.

// C program to demonstrate example of 
// Logical NOT (!) operator 

#include <stdio.h>

int main()
{
    int num =10;
    
    //printing result with OR (||) operator
    printf("%d\n", !(num==10));
    printf("%d\n", !(num!=10));
    printf("%d\n", !(num>5));
    printf("%d\n", !(num<5));
    
    return 0;
}

Output

Example 2

Input a year and check it is leap year or not (it will use Logical AND (&&), Logical OR (||) and Logical NOT (!) operators).

// C program to demonstrate example of 
// Logical NOT (!) operator 

// Input a year and check it is leap year or not 
#include <stdio.h>

int main()
{
    int y;
    
    //input year 
    printf("Enter year: ");
    scanf("%d", &y);
    
    //check condition
    if((y%400==0) || (y%4==0 && y%100!=0))
        printf("%d is a leap year\n",y);
    else
        printf("%d is not a leap year\n",y);
    
    return 0;
}