多态的一个例子

#include

#include

using namespace std;

 

class Item_base {

public:

       Item_base(string& book,double f):isbn(book),price(f) {}

       string book()

       {

              return isbn;

       }

       virtual double net_price(size_t n)

       {

               return n*price;

       }

      

private:

        string isbn;

protected:

        double price;

}; 

 

class Bulk_item:public Item_base {

public:

       Bulk_item(string book,double i): Item_base(book,i) {}

       double net_price(int n)

       {

              if (n >= count)

                 return n*(1-discount)*price;

              else

                  return n*price;

       }

private:

        size_t count;

        double discount;

};  

         

int main()

{

    string book="java";

    cout<<"基类对象的函数调用"<

    Item_base a(book,30);

    double total=a.net_price(2);

    cout<<"the total price are:"<

   

    book="c++";

    cout<<"派生类对象的函数调用"<

    Bulk_item b(book,40);

    total=b.net_price(2);

    cout<<"the total price are:"<

   

    cout<<"基类类型指针的不同指向"<

    Item_base *pa;

    pa=&a;

    total=pa->net_price(2);

    cout<<"the total price are:"<

   

    pa=&b;

    total=pa->net_price(2);

    cout<<"the total price are:"<

   

    cout<<"基类类型对象引用的不同绑定"<

    Item_base &sa=a;

    total=sa.net_price(2);

    cout<<"the total price are:"<

   

    Item_base &sa2=b;

    total=sa2.net_price(2);

    cout<<"the total price are:"<

   

    cout<<"派生类类型的指针的不同指向"<

    Bulk_item *pb;

    pb=static_cast(&a);

//    pb=dynamic_cast(&a);  ////此处运行时会报错

    total=pb->net_price(2);

    cout<<"the total price are:"<

   

    pb=&b;

    total=pb->net_price(2);

    cout<<"the total price are:"<

   

    getchar();

    return 0;

}