C++ primer plus Sales_item.h源码

Sales_item.h代码块

#ifndef SALESITEM_H
#define SALESITEM_H
#include <iostream>
#include <string>

class Sales_item
{
public:
Sales_item(const std::string &book):isbn(book),units_sold(0),revenue(0.0){}
Sales_item(std::istream &is){ is >> *this;}
friend std::istream& operator>>(std::istream &,Sales_item &);
friend std::ostream& operator<<(std::ostream &,const Sales_item &);
public:
Sales_item & operator+=(const Sales_item&);
public:
double avg_price() const;
bool same_isbn(const Sales_item &rhs)const
{
return isbn == rhs.isbn;
}
Sales_item():units_sold(0),revenue(0.0){}
public:
std::string isbn;
unsigned units_sold;
double revenue;
};

using std::istream;
using std::ostream;
Sales_item operator+(const Sales_item &,const Sales_item &);
inline bool operator==(const Sales_item &lhs,const Sales_item &rhs)
{
return lhs.units_sold == rhs.units_sold
&& lhs.revenue == rhs.revenue
&& lhs.same_isbn(rhs);
}
inline bool operator!=(const Sales_item &lhs,const Sales_item &rhs)
{
return !(lhs == rhs);
}

inline Sales_item & Sales_item::operator +=(const Sales_item &rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
}
inline Sales_item operator+(const Sales_item &lhs,const Sales_item &rhs)
{
Sales_item ret(lhs);
ret += rhs;
return ret;
}
inline istream& operator>>(istream &in,Sales_item &s)
{
double price;
in >> s.isbn >> s.units_sold >> price;
if(in)
s.revenue = s.units_sold * price;
else
s = Sales_item();
return in;
}
inline ostream& operator<<(ostream &out,const Sales_item &s)
{
out << s.isbn << "\t" <<s.units_sold << "\t" << s.revenue << "\t" << s.avg_price();
return out;
}
inline double Sales_item::avg_price() const
{
if(units_sold)
return revenue/units_sold;
else
return 0;
}
#endif

main.cpp代码块

#include <iostream>
#include "Sales_item.h"
int main(void)
{
Sales_item book;
//read ISBN, number of copies sold, and sales price
std::cin >> book;
//write ISBN, number of copies sold,
//total revenue, and average price
std::cout << book << std::endl;
return 0;
}

运行代码如下



运行结果说明：

第一行需要用户输入：

0-201-70353-X 4 23.99

表示书的编号是0-201-70353-X

卖出书的总数是4本

每本书的价格是23.99

下面一行是根据上一行用户输入信息计算输出的结果：

95.96是4本书的总价格，其他信息和上面相同