#include <iostream>
using namespace std;

class rational{
public:
    int n, d;
	rational():n(0),d(1){}
	rational(int a, int b=1):n(a),d(b){}
	// copy constructor
	rational(rational &r):n(r.n),d(r.d){}
	const rational operator+(const rational &rhs){
		int num = n*rhs.d + rhs.n*d;
		int den = d*rhs.d;
		return rational(num,den);
	}

	const rational operator-(const rational &rhs){
		int num = n*rhs.d - rhs.n*d;
		int den = d*rhs.d;
		return rational(num,den);
	}

	// show anonymous variable can call method
	rational setnd(int a, int b){
        return rational(a,b);
	}

	// assignment operator
	rational operator=(const rational &rhs){
		if(&rhs != this){ // do nothing if a = a
		   n = rhs.n;
		   d = rhs.d;
		}
		return *this;
	}
	friend ostream& operator<<(ostream &o, rational &r);
};

ostream& operator<<(ostream &o, rational &r){
	o << r.n <<"/" << r.d << " ";
	return o;
}

void main(){
    rational p(1,2), q(1,3), z(p);
	cout << p << " " << q << " " << z << endl;
	// prevent the following by making rational + return const
    // z = (p + q).setnd(3,4);
	z = p + q;
	cout << z << endl;
	z = p - q;
	cout << z << endl;
	z =  z + 1;// 1 is auto promoted to rational(1,1)
	cout << z << endl;
}