C++中的策略模式浅析

#include<iostream>
using namespace std;
#include<string>
//业务逻辑
//异常类用于处理异常情况
class opeException
{
public:
	void getMessage()
	{
		cout << "您的输入有误！" << endl;
	}
};
//运算类
class Operation
{
	//判断一个字符串是不是数字
	bool isStringNum(string& s)
	{
		bool flag = true;
		for (auto e : s)
			if (!(isdigit(e)))
			{
				flag = false;
				break;
			}
		return flag;
	}
protected:
	bool isError(string& _strNum1, string& _strNum2, string& _ope)
	{
		if (!(Operation::isStringNum(_strNum1) && Operation::isStringNum(_strNum2) && (_ope == "+" || _ope == "-" || _ope == "*" || _ope == "/")))
		{
			return false;
		}
	}
public:
	virtual int getResult()
	{
		return 0;
	}
};
//加法运算类
class addOperation :public Operation
{
private:
	string strNum1;
	string strNum2;
	string ope;
	int re;
public:
	addOperation(string& _strNum1, string& _strNum2, string& _ope) :strNum1(_strNum1), strNum2(_strNum2), ope(_ope), re(0) {}
	virtual int getResult() override
	{
		if (!isError(strNum1, strNum2, ope))
			throw opeException();
		else
			re = stoi(strNum1) + stoi(strNum2);
		return re;
	}
};
//减法运算类
class subOperation :public Operation
{
private:
	string strNum1;
	string strNum2;
	string ope;
	int re;
public:
	subOperation(string& _strNum1, string& _strNum2, string& _ope) :strNum1(_strNum1), strNum2(_strNum2), ope(_ope), re(0) {}
	virtual int getResult() override
	{
		if (!isError(strNum1, strNum2, ope))
			throw opeException();
		else
			re = stoi(strNum1) - stoi(strNum2);
		return re;
	}
};
//乘法运算类
class mulOperation :public Operation
{
private:
	string strNum1;
	string strNum2;
	string ope;
	int re;
public:
	mulOperation(string& _strNum1, string& _strNum2, string& _ope) :strNum1(_strNum1), strNum2(_strNum2), ope(_ope), re(0) {}
	virtual int getResult() override
	{
		if (!isError(strNum1, strNum2, ope))
			throw opeException();
		else
			re = stoi(strNum1) * stoi(strNum2);
		return re;
	}
};
//除法运算类
class divOperation :public Operation
{
private:
	string strNum1;
	string strNum2;
	string ope;
	int re;
public:
	divOperation(string& _strNum1, string& _strNum2, string& _ope) :strNum1(_strNum1), strNum2(_strNum2), ope(_ope), re(0) {}
	virtual int getResult() override
	{
		if (!isError(strNum1, strNum2, ope))
			throw opeException();
		else if (stoi(strNum2) != 0)
			re = stoi(strNum1) / stoi(strNum2);
		else
			throw opeException();
		return re;
	}
};
//Conetext结合简单工厂模式
class Context
{
	Operation *operation;
public:
	Context(string& _strNum1, string& _strNum2, string& _ope)
	{
		if (_ope == "+")
		{
			operation = new addOperation(_strNum1, _strNum2, _ope);
		}
		else if (_ope == "-")
			operation = new subOperation(_strNum1, _strNum2, _ope);
		else if (_ope == "*")
			operation = new mulOperation(_strNum1, _strNum2, _ope);
		else if (_ope == "/")
		{
			operation = new divOperation(_strNum1, _strNum2, _ope);
		}
		else
			operation = nullptr;
	}
	Operation* get()
	{
		return operation;
	}
	int contextResult()
	{
		return operation->getResult();
	}
};
//界面逻辑
int main()
{
	try
	{
		string _strNum1 = " ";
		string _strNum2 = " ";
		string _ope = " ";
		cout << "请输入左操作数：" << endl;
		cin >> _strNum1;
		cout << "请输入右操作数：" << endl;
		cin >> _strNum2;
		cout << "请输入操作符：" << endl;
		cin >> _ope;
		Context context(_strNum1, _strNum2, _ope);
		if (context.get() != nullptr)
			cout << context.contextResult() << endl;
		else
			cout << "您的输入有误！" << endl;
	}
	catch (opeException ex)
	{
		cout << "您的输入有误" << endl;
	}
	return 0;
}