第一章 开始

1.20

头文件：

#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, 561  
friend 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() = default;  
    Sales_item(const std::string &book): bookNo(book) { }  
    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 before  
private:  
    std::string bookNo;      // implicitly initialized to the empty string  
    unsigned units_sold;  // explicitly initialized  
    double revenue;  
};  
  
// used in chapter 10  
inline  
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)  
{ return lhs.isbn() == rhs.isbn(); }  
  
// nonmember binary operator: must declare a parameter for each operand  
Sales_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 ISBN  
Sales_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 ISBN  
Sales_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 

代码：

#include <iostream>
#include "Sales_item.h"
 
using namespace std;

int main()
{
    Sales_item book; 
    while (cin >> book) {
        cout << book << endl;
    }
    return 0;
}

1.21

#include <iostream>
#include "Sales_item.h"
 
using namespace std;

int main()
{
    Sales_item book1, book2; 
    while (cin >> book1 >> book2) {
        if (book1.isbn() == book2.isbn())
            cout << book1 + book2 << endl;
        else cout << "两本书的ISBN必须相同！
";
    }
    return 0;
}

1.22

#include <iostream>
#include "Sales_item.h"
 
using namespace std;

int main()
{
    Sales_item total, book;
    cin >> total;
    while (cin >> book) {
        if (total.isbn() != book.isbn())
            break;
        total += book;
    }
    cout << total << endl;
    return 0;
}

1.23&1.24

#include <iostream>
#include "Sales_item.h"
 
using namespace std;

int main()
{
    Sales_item cur, book;
    int cnt = 1;
    cin >> cur;
    while (cin >> book) {
        if (book.isbn() == cur.isbn()) {
            cnt++;
        }
        else {
            cout << cur.isbn() << "有" << cnt << "条销售记录。
";
            cnt = 1;
            cur = book; 
        }
    }
    return 0;
}

注：要保证同一个ISBN号的输入是相连的。