C++Primer第五版 1.5.1节练习

1. 题目

练习1.20 :在网站（书上提供）上，第一章的代码目录中包含了头文件Sales_item.h。将它拷贝到你自己的工作目录中。用它编写一个程序，读取一组书籍销售记录，将每条记录打印到标准输出上。

练习 1.21 :编写程序，读取两个ISBN相同的Sales_item对象，输出它们的和。

练习 1.22 :编写程序，读取多个具有相同ISBN的销售记录，输出其所有记录的和。

2.代码

Sales_item.h

/* * This file contains code from "C++ Primer, Fifth Edition", by Stanley B. * Lippman, Josee Lajoie, and Barbara E. Moo, and is covered under the * copyright and warranty notices given in that book: *  * "Copyright (c) 2013 by Objectwrite, Inc., Josee Lajoie, and Barbara E. Moo." *  *  * "The authors and publisher have taken care in the preparation of this book, * but make no expressed or implied warranty of any kind and assume no * responsibility for errors or omissions. No liability is assumed for * incidental or consequential damages in connection with or arising out of the * use of the information or programs contained herein." *  * Permission is granted for this code to be used for educational purposes in * association with the book, given proper citation if and when posted or * reproduced.Any commercial use of this code requires the explicit written * permission of the publisher, Addison-Wesley Professional, a division of * Pearson Education, Inc. Send your request for permission, stating clearly * what code you would like to use, and in what specific way, to the following * address:  *  *     Pearson Education, Inc. *     Rights and Permissions Department *     One Lake Street *     Upper Saddle River, NJ  07458 *     Fax: [phone]*/ /* This file defines the Sales_item class used in chapter 1. * The code used in this file will be explained in * Chapter 7 (Classes) and Chapter 14 (Overloaded Operators) * Readers shouldn't try to understand the code in this file * until they have read those chapters.*/#ifndef SALESITEM_H// we're here only if SALESITEM_H has not yet been defined #define SALESITEM_H// Definition of Sales_item class and related functions goes here#include <iostream>#include <string>class Sales_item {// these declarations are explained section 7.2.1, p. 270 // and in chapter 14, pages 557, 558, 561friend std::istream& operator>>(std::istream&, Sales_item&);friend std::ostream& operator<<(std::ostream&, const Sales_item&);friend bool operator<(const Sales_item&, const Sales_item&);friend bool operator==(const Sales_item&, const Sales_item&);public:    // constructors are explained in section 7.1.4, pages 262 - 265    // default constructor needed to initialize members of built-in type    Sales_item(): units_sold(0), revenue(0.0) { }    Sales_item(const std::string &book):                   bookNo(book), units_sold(0), revenue(0.0) { }    Sales_item(std::istream &is) { is >> *this; }public:    // operations on Sales_item objects    // member binary operator: left-hand operand bound to implicit this pointer    Sales_item& operator+=(const Sales_item&);    // operations on Sales_item objects    std::string isbn() const { return bookNo; }    double avg_price() const;// private members as beforeprivate:    std::string bookNo;      // implicitly initialized to the empty string    unsigned units_sold;    double revenue;};// used in chapter 10inlinebool compareIsbn(const Sales_item &lhs, const Sales_item &rhs) { return lhs.isbn() == rhs.isbn(); }// nonmember binary operator: must declare a parameter for each operandSales_item operator+(const Sales_item&, const Sales_item&);inline bool operator==(const Sales_item &lhs, const Sales_item &rhs){    // must be made a friend of Sales_item    return lhs.units_sold == rhs.units_sold &&           lhs.revenue == rhs.revenue &&           lhs.isbn() == rhs.isbn();}inline bool operator!=(const Sales_item &lhs, const Sales_item &rhs){    return !(lhs == rhs); // != defined in terms of operator==}// assumes that both objects refer to the same ISBNSales_item& Sales_item::operator+=(const Sales_item& rhs) {    units_sold += rhs.units_sold;     revenue += rhs.revenue;     return *this;}// assumes that both objects refer to the same ISBNSales_item operator+(const Sales_item& lhs, const Sales_item& rhs) {    Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return    ret += rhs;           // add in the contents of (|rhs|)     return ret;           // return (|ret|) by value}std::istream& operator>>(std::istream& in, Sales_item& s){    double price;    in >> s.bookNo >> s.units_sold >> price;    // check that the inputs succeeded    if (in)        s.revenue = s.units_sold * price;    else         s = Sales_item();  // input failed: reset object to default state    return in;}std::ostream& operator<<(std::ostream& out, const Sales_item& s){    out << s.isbn() << " " << s.units_sold << " "        << s.revenue << " " << s.avg_price();    return out;}double Sales_item::avg_price() const{    if (units_sold)         return revenue/units_sold;     else         return 0;}#endif

练习1.20

#include <iostream>#include "Sales_item.h" int main(int argc, char** argv) {    Sales_item item;    while (std::cin >> item)          std::cout << item << std::endl;    getchar();    return 0;}

练习1.21

#include <iostream>#include "Sales_item.h" using namespace std;int main(int argc, char** argv) {    Sales_item item1, item2;    std::cin >> item1 >> item2;    if(item1.isbn() == item2.isbn())        cout << item1 + item2 << endl;    else         cout << "Data is Error input" << endl;     getchar();    return 0;}

练习1.22

#include <iostream>#include "Sales_item.h" using namespace std;int main(int argc, char** argv) {    Sales_item item1, item2,item3,item4;    if((item1.isbn()) == (item2.isbn())&&(item2.isbn() ==item3.isbn())&&(item3.isbn() == item4.isbn()))    {        cout<<(item1 + item2 + item3 + item4)<<endl;    }    else         cout << "Data is Error input" << endl;     getchar();    return 0;}