设计模式案例（C++版）-- 策略模式

策略模式定义了一系列算法，分别封装起来，让他们之间可以互相替换，且算法的变化不会影响到使用算法的客户。
一.需求分析
某商场营业，收银员根据客户所购买商品单价和数量向客户收费。近日某些商品做活动，有两种打折方式：
1.根据折扣打八折；
2.满减，满300减100。
二.模块设计

context类中可以传入具体的打折策略，并根据策略的不同得到不同的收费结果。

三.代码实现

1.策略类

#ifndef CASHSUPER_H
#define CASHSUPER_H
/*
* 收费基类
*/
class CashSuper
{
public:
	//收费单价 数量
	virtual double acceptCash(double price, int num);
};
#endif

#include "CashSuper.h"

double CashSuper::acceptCash(double price, int num)
{
    return 0.0;
}

2.原价

#ifndef CASHNORMAL_H
#define CASHNORMAL_H
#include "CashSuper.h"
/*
* 原价
*/
class CashNormal :
    public CashSuper
{
    //收费单价 数量
    double acceptCash(double price, int num)override;
};
#endif

#include "CashNormal.h"

double CashNormal::acceptCash(double price, int num)
{
    return price * num;
}

3.打折

#ifndef CASHREBATE_H
#define CASHREBATE_H
#include "CashSuper.h"
/*
* 打七折
*/
class CashRebate :
    public CashSuper
{
public:

    CashRebate(double rebate);

    double acceptCash(double price, int num);
private:
    double m_rebate; //折扣率
};
#endif

#include "CashRebate.h"

CashRebate::CashRebate(double rebate)
{
	m_rebate = rebate;
}

double CashRebate::acceptCash(double price, int num)
{
	return price * num * m_rebate;
}

4.满减

#ifndef CASHRETURN_H
#define CASHRETURN_H
#include "CashSuper.h"
/*
* 返利
*/
class CashReturn :
    public CashSuper
{
public:
    CashReturn(double condition, double ret);

    double acceptCash(double price, int num);
private:
    double m_condition; //返利条件
    double m_return; //返利值
};
#endif

#include "CashReturn.h"

CashReturn::CashReturn(double condition, double ret)
{
	m_condition = condition;
	m_return = ret;
}

double CashReturn::acceptCash(double price, int num)
{
	double result = price * num;
	if (m_condition > 0 && result >= m_condition)
	{
		result = result - (result / m_condition) * m_return;
	}
	return result;
}

5.context上下文

#ifndef CASHCONTEXT_H
#define CASHCONTEXT_H
/*
* 管理策略
*/
#include"CashSuper.h"
#include"CashNormal.h"
#include"CashRebate.h"
#include"CashReturn.h"
class CashContext
{
public:
	CashContext(int cashType);

	double getResult(double price, double num);
private:
	CashSuper* m_cs;
};
#endif

#include "CashContext.h"

CashContext::CashContext(int cashType)
{
	m_cs = nullptr;

	switch (cashType)
	{
	case 1: //原价
		m_cs = new CashNormal();
		break;
	case 2: //八折
		m_cs = new CashRebate(0.8);
		break;
	case 3: //300返100
		m_cs = new CashReturn(300, 100);
		break;
	default:
		break;
	}
}

double CashContext::getResult(double price, double num)
{
	return m_cs->acceptCash(price,num);
}

5.主函数

#include <iostream>
#include"CashContext.h"
using namespace std;

int main()
{
    cout << "请输入单价：" << endl;
    double price = 0;
    cin >> price;

    cout << "请输入数量：" << endl;
    int num;
    cin >> num;

    cout << "请输入收费模式：" << endl;
    cout << "1.原价" << endl;
    cout << "2.八折" << endl;
    cout << "3.满300反100" << endl;
    int select = 0;
    cin >> select;

    CashContext* context = new CashContext(select);
    cout << "费用为：" << context->getResult(price, num);
    return 0;
}