运算符重载

• 为什么要使用运算符重载
  -C/C++的运算符，支持的数据类型，仅限于基本数据类型。

• 问题：一头牛+一头马 = ？（牛马神兽？）
  一个圆 +一个圆 = ？ （想要变成一个更大的圆）
  一头牛 – 一只羊 = ？ (想要变成4只羊，原始的以物易物：1头牛价值5只羊)

• 解决方案：
  使用运算符重载

使用成员函数重载运算符

• 需求：把牛肉换猪肉, 羊肉换猪肉
  规则：
  一斤牛肉：2斤猪肉
  一斤羊肉：3斤猪肉

 
Cow类

> Cow.h

#pragma once
class Pork;
class Sheep;	

class Cow{	//牛类
public:
	Cow(int weight = 0);

	//使用运算符重载, 实现 牛肉 + 牛肉 = 猪肉 
	Pork operator+(const Cow& cow);

	//使用运算符重载, 实现 牛肉 + 羊肉 = 猪肉 
	Pork operator+(const Sheep& sheep);
private:
	int weight;	//重量
};


_________________________________________________________________________________________________________________________________


> Cow.cpp

#include "Cow.h"
#include "Pork.h"
#include "Sheep.h"

Cow::Cow(int weight){
	this->weight = weight;
}

//一斤牛肉换两斤猪肉
Pork Cow::operator+(const Cow& cow){	
	return Pork((this->weight + cow.weight) * 2);
}

//一斤牛肉换两斤猪肉, 一斤羊肉换三斤猪肉
Pork Cow::operator+(const Sheep& sheep){
	int tmp = (this->weight * 2) + (sheep.getWeight() * 3);
	return Pork(tmp);
}

 
Sheep类

> Sheep.h

#pragma once

//羊类
class Sheep{
public:
	Sheep(int weight = 0);
	int getWeight() const;
private:
	int weight;	//重量
};

_________________________________________________________________________________________________________________________________

> Sheep.cpp

#include "Sheep.h"

Sheep::Sheep(int weight){
	this->weight = weight;
}

int Sheep::getWeight() const{
	return weight;
}

Pork类

> Pork.h

#pragma once
#include <string>
using namespace std;

class Pork{	//猪肉类
public:
	Pork(int weight = 0);
	string description() const;
private:
	int weight;
};

_________________________________________________________________________________________________________________________________

> Pork.cpp

#include <sstream>
#include "Pork.h"

Pork::Pork(int weight){
	this->weight = weight;
}

string Pork::description() const{
	stringstream ret;
	ret << this->weight << "斤";
	return ret.str();
}

main.cpp

#include <iostream>
#include <Windows.h>
#include "Cow.h"
#include "Pork.h"
#include "Sheep.h"
using namespace std;

int main(void) {
	Pork p1;
	Cow c1(100);
	Cow c2(200);
	Sheep s1(100);

	//调用运算符重载 Pork operator+(const Cow& cow);
	p1 = c1 + c2;
	cout << "牛 + 牛 = 猪肉:" << p1.description() << endl;

	//调用运算符重载 Pork operator+(const Sheep& c1);
	p1 = c1 + s1;
	cout << "牛 + 羊 = 猪肉:" << p1.description() << endl;

	//羊+牛会报错, 因为没有定义对应的羊+牛运算符重载
	//p1 = s1 + c1;

	system("pause");
	return 0;
}