Modulo Operator (%) in C/C++ with Examples

In C or C++, the modulo operator (also known as the modulus operator), denoted by %, is an arithmetic operator. The modulo division operator produces the remainder of an integer division which is also called the modulus of the operation.

Syntax of Modulus Operator

If x and y are integers, then the expression:

x % y;

pronounced as “x mod y”. For example, 10 % 2 will be pronounced as ” Ten mod Two”.

Return Value of Modulo Operator

• If y completely divides x, the result of the expression is 0.
• If x is not completely divisible by y, then the result will be the remainder in the range [0, y-1]
• (x % y) < (x / 2) ………if (x >= y)
• (x % y) = x ……… if (x < y)
• If y is 0, then division by zero is a compile-time error.

Example of Modulo Operator

Below is the C/C++ program to demonstrate the working of the modulo operator:

C++

// C++ Program to demonstrate the working of modulo operator
#include <iostream>

using namespace std;

// Driver code
int main(void)
{
    int x, y;

    int result;

    x = 3;
    y = 4;

    // using modulo operator
    result = x % y;
    cout << result << endl;

    result = y % x;
    cout << result << endl;

    // for different values
    x = 4;
    y = 2;

    result = x % y;
    cout << result;

    return 0;
}

//    This code is contributed by Mayank Tyagi

C

// C Program to illustrate the working of modulo operator
#include <stdio.h>

int main(void)
{
    int x, y;

    int result;

    x = 3;
    y = 4;
    // using modulo operator
    result = x % y;
    printf("%d", result);

    result = y % x;
    printf("\n%d", result);

    // for different values
    x = 4;
    y = 2;
    result = x % y;
    printf("\n%d", result);

    return 0;
}

Restrictions on the Modulo Operator

The modulo operator has few restrictions or limitations on it. The % modulus operator cannot be applied to floating-point numbers i.e. float or double. If you try to use the modulo operator with floating-point constants or variables, the compiler will produce an error.

Example 1: C/C++ program to demonstrate the restrictions of the modulo operator.

C++

// C++ Program to demonstrate the restrictions of modulo
// operator
#include <iostream>
using namespace std;

// Driver code
int main()
{
    float x, y;

    x = 2.3;
    y = 1.5;

    // modulo for floating point values
    result = x % y;
    cout << result;

    return 0;
}

// This code is contributed by Harshit Srivastava

C

// C Program to illustrate the working of modulo operator
#include <stdio.h>

int main(void)
{
    float x, y;

    float result;

    x = 2.3;
    y = 1.5;

    // modulo for floating point values
    result = x % y;
    printf("%f", result);

    return 0;
}

Output

Compilation Error in C code :- prog.c: In function 'main':
prog.c:19:16: error:
 invalid operands to binary % (have 'float' and 'float')
     result = x % y;
                ^           

Modulo Operator for Negative Operands

The sign of the result for the modulo operator is machine-dependent for negative operands, as the action takes as a result of underflow or overflow. 

Example 2: C/C++ program to demonstrate the modulo operator for negative operands.

C++

// C++ Program to demonstrate the working of the modulo
// operator for negative operands
#include <iostream>
using namespace std;

// Driver code
int main(void)
{
    int x, y;

    int result;

    x = -3;
    y = 4;

    // modulo for negative operands
    result = x % y;
    cout << result << endl;

    x = 4;
    y = -2;
    result = x % y;
    cout << result << endl;

    x = -3;
    y = -4;
    result = x % y;
    cout << result;

    return 0;
}

// This code is contributed by Harshit Srivastava

C

// C Program to illustrate the working of the modulo
// operator with negative operands
#include <stdio.h>

int main(void)
{
    int x, y;

    int result;

    x = -3;
    y = 4;

    // modulo for negative operands
    result = x % y;
    printf("%d", result);

    x = 4;
    y = -2;
    result = x % y;
    printf("\n%d", result);

    x = -3;
    y = -4;
    result = x % y;
    printf("\n%d", result);

    return 0;
}

Output

-3
0
-3

Note: The return value in this case is compiler dependent.

FAQs on Modulo Operator

Q1. Define mod.

Answer:

In C/C++ programming languages, mod refers to the mathematical operation in which one number is divided by another, and the remainder is returned.

It can be performed using modulo operator (%).

Q2. What is mod arithmetic?

Answer:

Mod arithmetic refers to the process in which a number keeps wrapping around a certain point in such a way that it is always less than that certain point. For example,

Consider the number n = 10 and the point p = 20.
When we increment n 10 times, it will be n = 20 but in modular arithmetic, it should ways be smaller that the specified point.

One way to do that is to use modulo operator as:

n++;
n  = n % p;

To learn more about modular aritimatic, refer to the article – Modular Arithmatic

Q3. What is the difference between modulo and divide operator?

Answer:

The major difference between modulo and division operator is that:

• Modulo Operator (%) returns the remainder after dividing one number with other.
• Divide Operator (/) returns the quotient after dividing one number with other.