<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">面向物件的優點：</span>

1、可維護：修改簡單

2、可複用：可以在多個模組重複使用

3、可擴充套件：可以方便地加入一些其他功能

4、靈活性好：可以適應不同的需求

簡單工廠模式：

對程式進行功能分析，不同功能模組獨立

對計算器的UML圖：

程式實現：

#include <iostream>
#include <string>
#include <memory>
class Operation
{
public:
	Operation() = default;
	Operation(double a, double b) : NumberA(a), NumberB(b) {}
	double NumberA;
	double NumberB;
	std::string Symbol;
	virtual double getResult() {
		return 0;
	}	 
};
class Add : public Operation
{
public:
	Add(double a, double b) :Operation(a, b) {}
	 double getResult() override {
		return NumberA + NumberA;
	}
};
class Sub :public Operation
{
public:
	Sub(double a, double b) :Operation(a, b) {}
	double getResult() override {
		return NumberA - NumberB;
	}
};
class Multiply : public Operation
{
public:
	Multiply(double a, double b) :Operation(a, b) {}
	double getResult() override {
		return NumberA * NumberB;
	}
};
class Divide : public Operation
{
public:
	Divide(double a, double b) :Operation(a, b) {}
	double getResult() override {
		double result = 0;
		return NumberA / NumberB;
	}
};
class Calculate
{
public:
	Calculate() = default;
	Operation oper;
	Operation* createOperation(std::istream &in) {
		std::string Symbol;
		std::cout << "PLZ enter number a, operations, number b !" << std::endl;
		in >> oper.NumberA >> Symbol >> oper.NumberB;
		if (Symbol == "+") 
			return new Add(oper.NumberA, oper.NumberB);
		if (Symbol == "-")
			return new Sub(oper.NumberA, oper.NumberB);
		if (Symbol == "*")
			return new Multiply(oper.NumberA, oper.NumberB);
		if (Symbol == "/" && oper.NumberB != 0)
			return new Divide(oper.NumberA, oper.NumberB);		
	}	
};

int main() {
	Calculate cal;
	Operation* op = cal.createOperation(std::cin);
	double result = op->getResult();
	std::cout << result << std::endl;
	delete op;
	return 0;
}