派生类的例子

#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

#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;
}

#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;
}