【设计模式】策略模式

#include <iostream>
using namespace std;
// 抽象策略基类
class Strategy {
public:
    virtual void Algorithm(const double lhs, const double rhs) = 0;
};
class StrategyAdd : public Strategy {
public:
    void Algorithm(const double lhs, const double rhs)
    {
        cout << lhs + rhs << endl;
    }
};
class StrategySub : public Strategy {
public:
    void Algorithm(const double lhs, const double rhs)
    {
        cout << lhs - rhs << endl;
    }
};
class StrategyMul : public Strategy {
public:
    void Algorithm(const double lhs, const double rhs)
    {
        cout << lhs * rhs << endl;
    }
};
class StrategyDiv : public Strategy {
public:
    void Algorithm(const double lhs, const double rhs)
    {
        if (rhs == 0)
            throw;
        cout << lhs / rhs << endl;
    }
};
// 给用户使用的类，包含某个策略
class Calculator {
public:
    Calculator(const char type)
    {
        // 利用工厂模式实例化策略
        switch (type)
        {
        case '+':
            strategy = new StrategyAdd();
            break;
        case '-':
            strategy = new StrategySub();
            break;
        case '*':
            strategy = new StrategyMul();
            break;
        case '/':
            strategy = new StrategyDiv();
            break;
        default:
            throw runtime_error("Invalid strategy!");
            break;
        }
    }
    ~Calculator()
    {
        delete strategy;    // 别忘记删除指针
    }
    // 该函数调用具体策略中的算法
    void Calculate(const double lhs, const double rhs)
    {
        strategy->Algorithm(lhs, rhs);
    }
private:
    Strategy *strategy; // 保存策略的指针
};
int main()
{
    Calculator add('+');
    Calculator sub('-');
    Calculator mul('*');
    Calculator div('/');
    
    add.Calculate(10, 20);
    sub.Calculate(30, 40);
    mul.Calculate(11, 11);
    div.Calculate(100, 8);
    system("pause");
    return 0;
}