#include<iostream>
using namespace std;

class Rational
{
private:
	int numerator;
	int denominator;
public:
	Rational(int n, int d) :numerator(n), denominator(d){}
	//乘法操作符既可以使用成員過載又可以使用友元過載的
	/*
	friend Rational operator *(const Rational &l, const Rational &r)
	{
		return Rational((l.numerator*r.numerator) , (l.denominator*r.denominator));
	}
	*/
	const Rational operator *(const Rational &r)
	{
		return Rational((this->numerator*r.numerator), (this->denominator*r.denominator));
	}
	//輸入輸出的操作符只能使用友元過載
	friend ostream & operator<<(ostream &o, Rational & r)
	{
		o << r.numerator << "/" << r.denominator << endl;
		return o;
	}
	//修改了物件r，故用const修飾是錯誤的，會導致過載失敗
	/*
	friend istream & operator>>(istream &i, const Rational & r)
	{
		char c;
		i >> r.numerator >> c >> r.denominator;
		return i;
	}
	*/
	
	friend istream &operator>>(istream &i, Rational &r)
	{ 
		char c; 
		i >> r.numerator >> c >> r.denominator; 
		return i; 
	}
}; 
int main()
{ 
	Rational r1(1, 2);
	Rational r2(3, 5);
	Rational res = r1*r2;
	cout << "r1:" << r1 << "r2:" << r2;
	cout << "r1*r2=" << res << endl;
	cin >> r1 >> r2; 
	cout << "r1:" << r1 << "r2:" << r2; 
	res = r1*r2; 
	cout << res << endl; 
	return 0; 
}