友员函数

#include <iostream>
using namespace std;
class Integer{
	int n;
public:
	Integer(int x = 0){ n = x; };
	friend int sum(Integer& a, Integer &b);
	friend class Operation;

};

int sum(Integer &a, Integer &b)
{
	return a.n + b.n;
}
class Operation
{
public:
	int sum(Integer &a, Integer &b){ return a.n + b.n; }
	int dif(Integer &a, Integer &b){ return a.n - b.n; }
	int product(Integer &a, Integer &b){ return a.n *b.n; }
	int ratio(Integer &a, Integer &b){ return a.n/ b.n; }
};
void main()
{
	Integer i(100), j(2);
	Operation z;
	cout << sum(i, j);
	cout << z.sum(i, j) << endl;
	cout << z.dif(i, j) << endl;
	cout << z.product(i, j) << endl;
	cout << z.ratio(i, j) << endl;
	getchar();
}