클래스 Book +=, -= 연산자 구현

#include <iostream>
#include <string>
using namespace std;

class Book {
	string title;
	int price, pages;
public:
	Book(string title = "", int price = 0, int pages = 0) {
		this->title = title;
		this->price = price;
		this->pages = pages;
	}
	void show() {
		cout << title << ' ' << price << "원 " << pages << " 페이지" << endl;
	}
	string getTitle() { return title; }
	friend Book& operator+=(Book& op1, int op2);
	friend Book& operator-=(Book& op1, int op2);
};

Book& operator+=(Book& op1, int op2) {
	op1.price += op2;
	return op1;
}

Book& operator-=(Book& op1, int op2) {
	op1.price -= op2;
	return op1;
}


int main() {
	cout << "2018305065 전유정" << endl << endl;

	Book b1("청춘", 20000, 300), b2("미래", 30000, 500);
	b1 += 500;
	b2 -= 500;
	b1.show();
	b2.show();
}