C :

#include<stdio.h>
int main(){
int m,n,temp;
scanf("%d %d",&m,&n);
while(m%n!=0){
  temp=n;
  n=m%n;
  m=temp;}
printf("%d\n",n);
return 0;
}

C++ :

#include <stdio.h>
int main() {
	int m, n, t;
	scanf("%d %d", &m, &n);
	/* 比较m和n的大小，通过交换保证m <= n */
	if (m > n) {
		t = m;
		m = n;
		n = t;
	}
	/* 进行欧几里得辗转相除法求出最大公约数，并保存在n中 */
	while (m != 0) {
		t = m;
		m = n % m;
		n = t;
	}
	printf("%d\n", n);
	return 0;
}

Java :

import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner cin = new Scanner(System.in);
		int m,n;
		int temp;
		m=cin.nextInt();
		n=cin.nextInt();
		if(m<n){
			temp=m;
			m=n;
			n=temp;
		}
		while(n!=0){
			temp=m%n;
			m=n;
			n=temp;
		}
		System.out.println(m);
	}
}