c++ primer Sales_item.h & 练习 1.20、1.21、1.22

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在网络上下载的 Sales_item.h如下：

#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

（Sales_item.h 与源代码在同一个文件夹下）

1.20

#include<iostream>#include "Sales_item.h"int main(){    Sales_item item_temp;        while(std::cin >> item_temp)        std::cout << item_temp << std::endl;    return 0;}

1.21

#include<iostream>#include "Sales_item.h"int main(){    Sales_item item1, item2;    std::cin >> item1 >> item2;    std::cout << item1 + item2 << std::endl;    return 0;}

1.22

#include<iostream>#include "Sales_item.h"int main(){        // currItem是我们正在统计的销售记录； 我们将读入的记录存入item    Sales_item currItem, item;    // 读取第一条记录， 并确保有记录可以处理    if(std::cin >> currItem) {        Sales_item sum_item = currItem;        // 保存已经统计的销售记录                while(std::cin >> item)                // 读取剩余记录            if(item.isbn == currItem.isbn)    // 如果书的isbn相同                sum_item += item;            // 将销售记录统计到sum_item        std::cout << sum_item << std::endl;    // 打印销售记录    }    return 0;}

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