大话设计模式一：代码无错就是优----简单工厂模式

/*
**计算机控制台程序
**要求体现面向对象的思想
*/
#include <iostream>
#include <string>
using namespace std;

//运算类（基类 抽象类）
class Operation
{
public:
	Operation(double _numberA = 0.0, double _numberB = 0.0)
		:numberA(_numberA), numberB(_numberB){}
	
	void SetNumberA(double _numberA)
	{
		numberA = _numberA;
	}

	void SetNumberB(double _numberB)
	{
		numberB = _numberB;
	}

	virtual double GetResult() = 0;

protected:
	double numberA;
	double numberB;
};

//加减乘除类（派生类）

//加
class OperationAdd : public Operation
{
public:
	double GetResult();
private:
	double result = 0.0;
};

double 
OperationAdd::GetResult()
{
	result = numberA + numberB;
	return result;
}

//减
class OperationSub : public Operation
{
public:
	double GetResult();
private:
	double result = 0.0;
};

double
OperationSub::GetResult()
{
	result = numberA - numberB;
	return result;
}

//乘
class OperationMul : public Operation
{
public:
	double GetResult();
private:
	double result = 0.0;
};

double
OperationMul::GetResult()
{
	result = numberA * numberB;
	return result;
}

//除
class OperationDiv : public Operation
{
public:
	double GetResult();
private:
	double result = 0.0;
};

double
OperationDiv::GetResult()
{
	if (numberB == 0)
		throw;
	result = numberA / numberB;
	return result;
}

//运算工厂函数
Operation* createOperate(char operate)
{
	Operation *oper = NULL;
	switch (operate)
	{
	case '+':
		oper = new OperationAdd;
		break;
	case '-':
		oper = new OperationSub;
		break;
	case '*':
		oper = new OperationMul;
		break;
	case '/':
		oper = new OperationDiv;
		break;
	}
	return oper;
}

int main()
{
	double numberA, numberB, result;
	char c;
	cout << "numberA = ";
	cin >> numberA;
	cout << " numberB = ";
	cin >> numberB;
	cout << endl;
	cout << "what do you want to do? ";
	cin >> c;

	Operation* oper = createOperate(c);
	oper->SetNumberA(numberA);
	oper->SetNumberB(numberB);
	result = oper->GetResult();
	
	cout << " result is：" << result << endl;

}