代码记录

设计模式的代码注意要运用到面向对象的思想 考虑到紧耦合和松耦合
把具体的操作类分开 不让其互相影响（注意这点）
下面是UML类图

代码部分

#include <iostream>  
#include <memory> // 引入智能指针的头文件  

using namespace std;

// 操作基类  
class Operate {
public:
    Operate() {}
    virtual ~Operate() {}

    virtual int GetResult() = 0; // 纯虚函数，强制派生类实现  
    void  SetNumsA(int A)
    {
        NumsA = A;
    }
    void SetNumsB(int B)
    {
        NumsB = B;
    }
protected:
    int NumsA, NumsB;
};

// 加法操作类  
class AddOperate : public Operate {
public:
    int GetResult() override {
        return NumsA + NumsB;
    }
};

// 减法操作类  
class SubOperate : public Operate {
public:
    int GetResult() override {
        return NumsA - NumsB;
    }
};

// 乘法操作类  
class MulOperate : public Operate {
public:
    int GetResult() override {
        return NumsA * NumsB;
    }
};

// 除法操作类  
class DivOperate : public Operate {
public:
    int GetResult() override {
        if (NumsB == 0) {
            throw runtime_error("Division by zero is not allowed.");
        }
        return NumsA / NumsB;
    }
};

// 操作工厂类  
class OperateFactory {
public:
    OperateFactory() {}

    std::unique_ptr<Operate> CreateOperate(char op) {
        switch (op) {
        case '+': return std::make_unique<AddOperate>();
        case '-': return std::make_unique<SubOperate>();
        case '*': return std::make_unique<MulOperate>();
        case '/': return std::make_unique<DivOperate>();
        default:
            throw runtime_error("No such operation!");
        }
    }
};

int main() {
    try {
        OperateFactory factory;
        char op = '/';
        int numA = 100, numB = 700;

        std::unique_ptr<Operate> operate = factory.CreateOperate(op);
        operate->SetNumsA(numA);
        operate->SetNumsB(0);

        cout << operate->GetResult() << endl;
    }
    catch (const exception& e) {
        cout << "Error: " << e.what() << endl;
    }

    return 0;
}

代码参考书：
大话设计模式