大话设计模式——简单工厂模式（C++实现）

将《大话设计模式》书中的简单工厂模式（Simple Factory）用C++代码重写了一遍，如有错误，望指正。

SimpleFactory.h:

#ifndef _SIMPLEFACTORY_H
#define _SIMPLEFACTORY_H

//运用简单工厂模式设计一个计算器
#include <iostream>
#include <string>

using namespace std;

class COperation
{
public:
	COperation();
	virtual double GetResult();	//设置为虚函数，从而在子类中重载它
	double m_dNumA;
	double m_dNumB;
protected:
private:

};

class COperationAdd : public COperation
{
public:
	double GetResult();
protected:
private:
};

class COperationSub : public COperation
{
public:
	double GetResult();
protected:
private:
};

class COperationMul : public COperation
{
public:
	double GetResult();
protected:
private:
};

class COperationDiv : public COperation
{
public:
	double GetResult();
protected:
private:
};

class COperationFactory		//工厂类
{
public:
	COperation* CreateOperation(const char &ch);
protected:
private:
};
#endif

SimpleFactory.cpp:

#include "SimpleFactory.h"
/************************************************************************/
/* COperation类                                                         */
/************************************************************************/
double COperation::GetResult()
{
	double result = 0;
	return result;
}

COperation::COperation()
{
	m_dNumA = 0;
	m_dNumB = 0;
}
/************************************************************************/
/* COperationAdd类                                                      */
/************************************************************************/
double COperationAdd::GetResult()
{
	double result = m_dNumA + m_dNumB ;
	return result;
}

/************************************************************************/
/* COperationSub类                                                      */
/************************************************************************/
double COperationSub::GetResult()
{
	double result = m_dNumA - m_dNumB ;
	return result;
}

/************************************************************************/
/* COperationMul类                                                      */
/************************************************************************/
double COperationMul::GetResult()
{
	double result = m_dNumA * m_dNumB ;
	return result;
}

/************************************************************************/
/* COperationDiv类                                                      */
/************************************************************************/
double COperationDiv::GetResult()
{

	double result = 0 ;
	if (m_dNumB != 0)
		result =  m_dNumA / m_dNumB;
	else
		result = 999999999;
	return result;
}

/************************************************************************/
/* COperationFactory类                                                  */
/************************************************************************/
COperation* COperationFactory::CreateOperation(const char &ch)
{
	COperation *oper;
	switch (ch)
	{
	case '+':
		oper = new COperationAdd;
		break;
	case '-':
		oper = new COperationSub;
		break;
	case '*':
		oper = new COperationMul;
		break;
	case '/':
		oper = new COperationDiv;
		break;
	}
	return oper;
}

main.cpp:

#include <iostream>
#include "SimpleFactory.h"
using namespace std;


int main()
{
	COperationFactory factory;
	COperation *opr = factory.CreateOperation('*');
	opr->m_dNumA=1;
	opr->m_dNumB=2;
	cout<<opr->GetResult()<<endl;
	delete []opr;
	return 0;
}