프렌드와 연산자 중복

전위연산자는 참조매개변수를 써서 값을 바로 바꿔준다 

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

class Power {
	int kick;
	int punch;
public:
	Power(int kick = 0, int punch = 0) {
		this->kick = kick;
		this->punch = punch;
	}
	void show();
	friend Power& operator++(Power& op);
	friend Power operator++(Power& op, int x);
};

void Power::show() {
	cout << "kick" << kick << ", punch" << punch << endl;
}
Power& operator++(Power& op) {
	op.kick++;
	op.punch++;
	return op;
}
Power operator++(Power& op, int x) {
	Power tmp = op;
	op.kick++;
	op.punch++;
	return tmp;
}

int main() {
	Power a(3,5), b;
	b = ++a;
	a.show();
	b.show();
	b = a++;
	a.show(); b.show();
}