C :

#include <stdio.h>
int main()
{
  int a, b, i;
  scanf("%d %d", &a, &b);
  for(i = a ; i >= 1; i --)
  {
    if(a % i == 0 && b % i == 0)
    {
      printf("%d\n", i);
      break;
    }
  }
  return 0;
}

C++ :

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