能看看怎么改吗，c++

#include
using namespace std;
int gcd(int);
int main() {
int m, n,x,a;
cout << "请输入两个数m n：";
cin >> m >> n;
x = gcd(a);
cout << x << endl;
}
int gcd(int m,int n) {
int a;
for (int i = 1;i <= m && i <= n;i++) {
if (m % i == 0 && n % i == 0)
a = i;
}
return a;
}

x = gcd(a); 改成 x = gcd(m, n);