C++设计模式：简单工厂模式

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

class Operation
{
protected:
double _numberA;
double _numberB;
public:

Operation() :_numberA(0.0), _numberB(0.0)
{}
void SetNumberA(double number)
{
_numberA = number;
}
void SetNumberB(double number)
{
_numberB = number;
}

double GetNumberA()
{
return _numberA;
}
double GetNumberB()
{
return _numberB;
}

virtual double GetResult() = 0;
};

class OperationAdd :public Operation
{
double GetResult()
{
return _numberA + _numberB;
}
};

class OperationSub :public Operation
{
double GetResult()
{
return _numberA - _numberB;
}
};

class OperationMul :public Operation
{
double GetResult()
{
return _numberA*_numberB;
}
};

class OperationDiv :public Operation
{
double GetResult()
{
if (abs(_numberB) > 0.0001)
return _numberA / _numberB;
else
throw("除数不能为0");

}
};

class OperationFactory
{
public:
static Operation* createOperator(string operate)
{
Operation* oper = NULL;

if (operate == "+")
{
oper = new OperationAdd();
}
else if (operate == "-")
{
oper = new OperationSub();
}
else if (operate == "*")
{
oper = new OperationMul();
}
else if (operate == "/")
{
oper = new OperationDiv();
}

return oper;

}

private:

};

int main()
{
Operation*oper;
oper = OperationFactory::createOperator("+");
oper->SetNumberA(14);
oper->SetNumberA(34);

double result = oper->GetResult();

cout << result;

return 0;
}