ห.ร.ม.

#include <stdio.h>
int main(void) {
    int left = 48, right = 18;
    // Reduce the pair until no remainder remains.
    while (right) { int remainder = left % right; left = right; right = remainder; }
    printf("gcd=%d\n", left);
}

#include <iostream>
#include <numeric>
int main() {
    // std::gcd implements Euclid's algorithm.
    std::cout << "gcd=" << std::gcd(48, 18) << '\n';
}