派生类的例子

15.7定义一个类使其实现一种数量受限的折扣策略，具体策略是：当购买书籍的数量不超过一个给定的限量时享受折扣，如果购买量一旦超过了限量，则超出的部分将以原价销售。

Quote.h

#ifndef QUOTE_H

#define QUOTE_H

#include<iostream>

#include<string>

using namespace std;

class Quote

{

public:

    Quote()=default;

    Quote(const string &book,double sales_price):bookNo(book),price(sales_price) {}

    string isbn() const  {return bookNo;}

    virtual double net_price(size_t n) const

    { return n*price;}

    virtual ~Quote()=default;

private:

    string bookNo;

protected:

    double price=0.0;

};

class Bulk_quote:public Quote

{

public:

    Bulk_quote()=default;

    Bulk_quote(const string &, double , size_t , double );

    double net_price(size_t) const override;

private:

    size_t min_qty=0;

    double discount=0.0;

};

#endif // QUOTE_H

Quote.cpp

#include"Quote.h"

Bulk_quote::Bulk_quote(const string &book, double p, size_t qty, double disc):Quote(book,p),min_qty(qty),discount(disc) {}



double Bulk_quote::net_price(size_t cnt) const

{

    if(cnt<=min_qty)

        return cnt*(1-discount)*price;

    else

        return (cnt-min_qty)*price+min_qty*(1-discount)*price;

}

main.cpp

#include <iostream>

#include"Quote.h"

using namespace std;



double print_total(ostream &os,const Quote &item,size_t n)

{

    double ret=item.net_price(n);

    os<<"ISBN: "<<item.isbn()<<" # sold: "<<n<<" total due: "<<ret<<endl;

    return ret;

}

int main()

{

    Quote quote("Base",2);

    Bulk_quote bulk("devired",2,5,0.5);

    print_total(cout,quote,6);

    print_total(cout,bulk,6);

    return 0;

}