第七章类

 1 #include<iostream>
 2 #include<string>
 3 using namespace std;
 4 class Sales_data
 5 {
 6     friend  Sales_data add(const Sales_data &, const Sales_data &);
 7     friend  istream &read(istream &, Sales_data &);
 8     friend  ostream &print(ostream &, const Sales_data &);
 9 
10 public:
11     Sales_data() = default;       //构造函数
12     Sales_data(const string &s) :bookNo(s) {}
13     Sales_data(const string &s, unsigned n, double p) :bookNo(s), units_sold(n), revenue(p*n) {}
14     Sales_data(istream &);
15 
16 
17     string isbn() const { return bookNo; }  //相当于 string isbn () const { return this -> bookN0 }
18     Sales_data &combine(const Sales_data &);
19 
20 private:
21     double avg_price() const;
22     string bookNo;         //书ISBN编号
23     unsigned units_sold = 0;   //书籍销量
24     double revenue = 0.0;        //书籍销售收入
25 };
26 
27 Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
28 {
29     Sales_data sum = lhs;
30     sum.combine(rhs);
31     return sum;
32 }
33 istream &read(istream &is, Sales_data &item)
34 {
35     double price = 0;
36     is >> item.bookNo >> item.units_sold >> price;
37     item.revenue = item.units_sold * price;
38     return is;
39 }
40 
41 ostream &print(ostream &os, const Sales_data &item)
42 {
43     os << item.isbn() << " " << item.units_sold << " "
44         << item.revenue << " " << item.avg_price();
45     return os;
46 }
47 
48 Sales_data::Sales_data(istream &is)
49 {
50     read(is, *this);
51 }
52 Sales_data& Sales_data::combine(const Sales_data &rhs)
53 {
54     units_sold += rhs.units_sold;
55     revenue += rhs.revenue;
56     return *this;
57 }
58 
59 double Sales_data::avg_price() const
60 {
61     if (units_sold)
62         return revenue / units_sold;
63     else
64         return 0;
65 }

 1 #include<iostream>
 2 #include"Sales_data.h"
 3 
 4 using namespace std;
 5 int main()
 6 {
 7     Sales_data total;
 8     if (read(cin, total))
 9     {
10         Sales_data trans;
11         while (read(cin, trans))
12         {
13             if (total.isbn() == trans.isbn())
14                 total.combine(trans);
15             else
16             {
17                 print(cout, total) << endl;
18                 total = trans;
19             }
20         }
21         print(cout, total) << endl;
22     }
23     else
24     {
25         cerr << "NO data?" << endl;
26     }
27 }