Sales_item.h

#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;elses = 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;elsereturn 0;}#endif