简单工厂模式

根据不同的需求派生不同子类，然后在工厂类中生成对应对象。

// 创建工厂
class AbstractCalculator{};
class AddCalculator : public AbstractCalculator{};
class SubCalculator : public AbstractCalculator{};
class MulCalculator : public AbstractCalculator{};
class DivCalculator : public AbstractCalculator{};
class OperatorFactory{   
public:
AbstractCalculator* creatOperate(string str){
    AbstractCalculator *oper = NULL;
    if(str == "+"){
        oper = new(AddCalculator);
    }else if (str == "-"){
        oper= new(SubCalculator);
    }else if (str == "*"){
        oper = new(MulCalculator);
    }else if (str == "/"){
        oper = new(DivCalculator);
    }else{
        cout << "false!!!!!" << endl;
    }
    return oper;
}
};
// 主函数
auto main() -> int {
    AbstractCalculator *oper;
    OperatorFactory factory;
    oper = factory.creatOperate("+");
    oper->m_Num1 = 1999;
    oper->m_Num2 = 7234.44;
    cout << oper->m_Num1 << " + " << oper->m_Num2 << " = " << oper->getResult() << endl;
    return 0;
}