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This article will demonstrate various ways of using the modulo operator in C.

%Using the modulo operator in C to calculate the remainder in division

The modulo operator %is one of the binary arithmetic operators in C language. It produces the remainder after dividing two given numbers. The modulo operator cannot be applied to floating point numbers like floator double. In the following sample code, we show %the simplest example of using the operator, printing the result of taking the given intarray modulo 9.

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int arr[8] = {10, 24, 17, 35, 65, 89, 55, 77};

    for (int i = 0; i < 8; ++i) {
        printf("%d/%d yields the remainder of - %d\n", arr[i], 9, arr[i] % 9);
    }

    exit(EXIT_SUCCESS);
}

Output:

10/9 yields the remainder of - 1
24/9 yields the remainder of - 6
17/9 yields the remainder of - 8
35/9 yields the remainder of - 8
65/9 yields the remainder of - 2
89/9 yields the remainder of - 8
55/9 yields the remainder of - 1
77/9 yields the remainder of - 5

Using %the modulo operator to implement leap year check in C

In addition, we can also use %operators to implement more complex functions. The next example code demonstrates isLeapYearthe Boolean function, which checks whether a given year is a leap year. It is important to note that if a year value is divisible by 4 but not by 100, then the year is considered a leap year. In addition, if the year value is divisible by 400, it is a leap year.

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

bool isLeapYear(int year) {
    if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)
        return true;
    else
        return false;
}

int main(void) {

    uint year = 2021;
    isLeapYear(year) ?
        printf("%d is leap\n", year) :
        printf("%d is not leap\n", year);

    exit(EXIT_SUCCESS);
}

Output:

2021 is not leap

Use the modulo operator in C %to generate random numbers within a given integer range

Another useful function of the modulus operator is to place an upper limit on the number that can be generated during random number generation. That is, suppose we have a function that generates a random integer. In this case, we can take the remainder of the divisor between the returned number and the value we want as the maximum (defined as MAXthe macro in the example below). It should be noted that using the srandand randfunctions to generate random numbers is not a robust approach, and applications that require high-quality random numbers should use other tools.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define COUNT 10
#define MAX 100

int main(void) {

    srand(time(NULL));
    for (int i = 0; i < COUNT; i++) {
        printf("%d, ", rand() % MAX);
    }
    printf("\b\b  \n");

    exit(EXIT_SUCCESS);
}

Output:

3, 76, 74, 93, 51, 65, 76, 31, 61, 97