15.14

//15.14 重新定义bulk_item和item_base类，使每个类只需定义一个构造函数#include<iostream>#include<string>using namespace std;class item_base{public:item_base(const string &book="",double sales_price=0.0):isbn(book),price(sales_price){}string book()const{return isbn;}virtual double net_price(size_t)const{return price*n;}virtual ~item_base(){}private:string isbn;protected:double price;};class bulk_item :public item_base{public:bulk_item(const string &book="",double sales_price=0.0,size_t qty=0,double disc=0.0):item_base(book,sales_price),min_qty(qty),discount(disc){}double net_price(size_t cnt)const{if (cnt > min_qty)return cnt*(1 - discount)*price;elsereturn cnt *price;}private:size_t min_qty;double discount;};