请问怎样把f值返回给s

#include "iosrtream.h"
class aa
{ public:
aa(int x,int y)
{
int f;
f=x+y;
}
}
main()
{
int x=1,y=2,s;
aa(x,y);
s=aa(x,y);
}

 #include <iostream>
using namespace std;

class aa
{ 
private:
    int f;
public:
    aa(int x,int y)
    {
      f = x + y;
    }
    int getf() { return f; }
};
int main()
{
    int x = 1, y = 2, s;
    aa a(x, y);
    s = a.getf();
    cout << s << endl;
}

神一般的主函数，你难道没学过类吗？