用递归的方法求两个数的最大公约数

#include<stdio.h>
int gcd(int m, int n)
{
int r = 0;
r = m%n;
if (r<0)
return 0;
else if (r == 0)
return n;
else if (r>0)
return  gcd(n, r);
}
int main()
{
int N = 0;
int M = 0;
int gc = 0;
scanf("%d%d", &N, &M);
gc = gcd(M, N);
printf("%d\n", gc);

system("pause");
return 0;
}