Common Factors of Two Numbers in C

Common factors are integers that divide two numbers exactly. For example, the positive common factors of 12 and 18 are 1, 2, 3 and 6.

Display Common Factors of Two Numbers Top ↑

#include <stdio.h>

void common_factors(int first, int second) {
    if (first < 0) {
        first = -first;
    }

    if (second < 0) {
        second = -second;
    }

    if (first == 0 && second == 0) {
        printf("0 and 0 do not have a finite list of common factors.\n");
        return;
    }

    int limit = first < second ? first : second;

    if (limit == 0) {
        limit = first > second ? first : second;
    }

    printf("Common factors: ");

    for (int i = 1; i <= limit; i++) {
        if (first % i == 0 && second % i == 0) {
            printf("%d ", i);
        }
    }

    putchar('\n');
}

int main(void) {
    int first = 12;
    int second = 18;

    common_factors(first, second);
    return 0;
}

Output

Common factors: 1 2 3 6

Read Both Numbers from the User Top ↑

#include <stdio.h>

int main(void) {
    int first;
    int second;

    printf("Enter two integers: ");
    if (scanf("%d %d", &first, &second) != 2) {
        printf("Invalid input.\n");
        return 1;
    }

    if (first < 0) first = -first;
    if (second < 0) second = -second;

    if (first == 0 && second == 0) {
        printf("No finite common-factor list for 0 and 0.\n");
        return 0;
    }

    int limit = first < second ? first : second;

    if (limit == 0) {
        limit = first > second ? first : second;
    }

    for (int i = 1; i <= limit; i++) {
        if (first % i == 0 && second % i == 0) {
            printf("%d ", i);
        }
    }

    putchar('\n');
    return 0;
}

Common Factors vs Highest Common Factor Top ↑

This page lists every positive common factor. If you only need the largest one, use the more efficient Euclidean algorithm on the HCF / GCD page.

Subhendu Mohapatra

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I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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