大话设计模式——简单工厂模式

书上使用c#实现的，我改成了c++,本人属于菜鸟级别，如有错误还请留言指教

#include <iostream>
#include <string>
using namespace std;

class Operation
{
	public:
		double A;
		double B;
		virtual double GetResult()
		{
			
		};
};
class OperationAdd : public Operation
{
	public:
		virtual double GetResult()
		{
			double result = 0;
			result = A + B;
			return result;
		};	
};
class OperationSub : public Operation
{
	public:
		virtual double GetResult()
		{
			double result = 0;
			result = A - B;
			return result;
		};	
};
class OperationMul : public Operation
{
	public:
		virtual double GetResult()
		{
			double result = 0;
			result = A * B;
			return result;
		};		
};
class OperationDiv : public Operation
{
	public:
		virtual double GetResult()
		{
			double result = 0;
			if( B == 0 )
			{
				//throw new Exception( "wrong");
				cerr << "wrong" << endl;
			}
			result = A / B;
			return result;
		};	
};
class OperationFactory
{
	public:
		Operation* createOperate( int operate )
		{
			Operation *oper = NULL;
			switch( operate )
			{
				case 1:
					oper = new OperationAdd();
					break;
				case 2:
					oper = new OperationSub();	
					break;
				case 3:
					oper = new OperationMul();  	
					break;
				case 4:
					oper = new OperationDiv(); 	
					break;
			}
			return oper;
		}
};

int main()
{
	Operation *oper;
	OperationFactory choose;
	oper = choose.createOperate( 1 );
	oper->A = 1;
	oper->B = 2;
	double result = oper->GetResult();
	cout << result << endl;
        return 0;
}