第一章开始

1.20

头文件：

  1 #ifndef SALESITEM_H  
  2 // we're here only if SALESITEM_H has not yet been defined  
  3 #define SALESITEM_H  
  4   
  5 // Definition of Sales_item class and related functions goes here  
  6 #include <iostream>  
  7 #include <string>  
  8   
  9 class Sales_item {  
 10 // these declarations are explained section 7.2.1, p. 270  
 11 // and in chapter 14, pages 557, 558, 561  
 12 friend std::istream& operator>>(std::istream&, Sales_item&);  
 13 friend std::ostream& operator<<(std::ostream&, const Sales_item&);  
 14 friend bool operator<(const Sales_item&, const Sales_item&);  
 15 friend bool  
 16 operator==(const Sales_item&, const Sales_item&);  
 17 public:  
 18     // constructors are explained in section 7.1.4, pages 262 - 265  
 19     // default constructor needed to initialize members of built-in type  
 20     Sales_item() = default;  
 21     Sales_item(const std::string &book): bookNo(book) { }  
 22     Sales_item(std::istream &is) { is >> *this; }  
 23 public:  
 24     // operations on Sales_item objects  
 25     // member binary operator: left-hand operand bound to implicit this pointer  
 26     Sales_item& operator+=(const Sales_item&);  
 27   
 28     // operations on Sales_item objects  
 29     std::string isbn() const { return bookNo; }  
 30     double avg_price() const;  
 31 // private members as before  
 32 private:  
 33     std::string bookNo;      // implicitly initialized to the empty string  
 34     unsigned units_sold;  // explicitly initialized  
 35     double revenue;  
 36 };  
 37   
 38 // used in chapter 10  
 39 inline  
 40 bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)  
 41 { return lhs.isbn() == rhs.isbn(); }  
 42   
 43 // nonmember binary operator: must declare a parameter for each operand  
 44 Sales_item operator+(const Sales_item&, const Sales_item&);  
 45   
 46 inline bool  
 47 operator==(const Sales_item &lhs, const Sales_item &rhs)  
 48 {  
 49     // must be made a friend of Sales_item  
 50     return lhs.units_sold == rhs.units_sold &&  
 51            lhs.revenue == rhs.revenue &&  
 52            lhs.isbn() == rhs.isbn();  
 53 }  
 54   
 55 inline bool  
 56 operator!=(const Sales_item &lhs, const Sales_item &rhs)  
 57 {  
 58     return !(lhs == rhs); // != defined in terms of operator==  
 59 }  
 60   
 61 // assumes that both objects refer to the same ISBN  
 62 Sales_item& Sales_item::operator+=(const Sales_item& rhs)  
 63 {  
 64     units_sold += rhs.units_sold;  
 65     revenue += rhs.revenue;  
 66     return *this;  
 67 }  
 68   
 69 // assumes that both objects refer to the same ISBN  
 70 Sales_item  
 71 operator+(const Sales_item& lhs, const Sales_item& rhs)  
 72 {  
 73     Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return  
 74     ret += rhs;           // add in the contents of (|rhs|)  
 75     return ret;           // return (|ret|) by value  
 76 }  
 77   
 78 std::istream&  
 79 operator>>(std::istream& in, Sales_item& s)  
 80 {  
 81     double price;  
 82     in >> s.bookNo >> s.units_sold >> price;  
 83     // check that the inputs succeeded  
 84     if (in)  
 85         s.revenue = s.units_sold * price;  
 86     else  
 87         s = Sales_item();  // input failed: reset object to default state  
 88     return in;  
 89 }  
 90   
 91 std::ostream&  
 92 operator<<(std::ostream& out, const Sales_item& s)  
 93 {  
 94     out << s.isbn() << " " << s.units_sold << " "  
 95         << s.revenue << " " << s.avg_price();  
 96     return out;  
 97 }  
 98   
 99 double Sales_item::avg_price() const  
100 {  
101     if (units_sold)  
102         return revenue/units_sold;  
103     else  
104         return 0;  
105 }  
106 #endif

Sales_item.h

代码：

 1 #include <iostream>
 2 #include "Sales_item.h"
 3  
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     Sales_item book; 
 9     while (cin >> book) {
10         cout << book << endl;
11     }
12     return 0;
13 }

View Code

1.21

 1 #include <iostream>
 2 #include "Sales_item.h"
 3  
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     Sales_item book1, book2; 
 9     while (cin >> book1 >> book2) {
10         if (book1.isbn() == book2.isbn())
11             cout << book1 + book2 << endl;
12         else cout << "两本书的ISBN必须相同！
";
13     }
14     return 0;
15 }

View Code

1.22

 1 #include <iostream>
 2 #include "Sales_item.h"
 3  
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     Sales_item total, book;
 9     cin >> total;
10     while (cin >> book) {
11         if (total.isbn() != book.isbn())
12             break;
13         total += book;
14     }
15     cout << total << endl;
16     return 0;
17 }

View Code

1.23&1.24

 1 #include <iostream>
 2 #include "Sales_item.h"
 3  
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     Sales_item cur, book;
 9     int cnt = 1;
10     cin >> cur;
11     while (cin >> book) {
12         if (book.isbn() == cur.isbn()) {
13             cnt++;
14         }
15         else {
16             cout << cur.isbn() << "有" << cnt << "条销售记录。
";
17             cnt = 1;
18             cur = book; 
19         }
20     }
21     return 0;
22 }

View Code

注：要保证同一个ISBN号的输入是相连的。

第一章 开始

第一章开始