C++primer 15.4节练习

练习15.15、练习15.16

 1 #include <iostream>
 2 #include <string>
 3 #include <utility>
 4 #include <memory>
 5 #include <vector>
 6
 7 using namespace std;
 8
 9 class Quote {
10 public:
11     Quote() = default;
12     Quote(const string &book, double sales_price) : bookNo(book), price(sales_price) {}
13     const string& isbn() const { return bookNo; }
14     virtual double net_price(size_t n) const{ return n * price; }
15     virtual ~Quote() = default;
16 private:
17     string bookNo;
18 protected:
19     double price = 0.0;
20 };
21
22 class Disc_quote : public Quote{
23 public:
24     Disc_quote() = default;
25     Disc_quote(const string &book, double sales_price, size_t quan, double dis) : Quote(book, sales_price), quantity(quan), discount(dis) {}
26     double net_price(size_t n) const = 0;
27 protected:
28     size_t quantity = 0;
29     double discount = 0.0;
30 };
31
32 class Bulk_quote : public Disc_quote {
33 public:
34     Bulk_quote() = default;
35     Bulk_quote(const string& book, double p, size_t qty, double disc) : Disc_quote(book, p, qty, disc) {}
36     double net_price(size_t n) const override;
37 };
38
39 class lim_discount : public Disc_quote {
40 public:
41     lim_discount() = default;
42     lim_discount(const string& book, double p, size_t qty, double disc) : Disc_quote(book, p, qty, disc) {}
43     double net_price(size_t n) const override;
44 };
45
46 double print_total(ostream& os, const Quote& item, size_t t);
47
48 int main()
49 {
50     Bulk_quote b1("C++ primer", 128.0, 10, 0.60);
51     lim_discount l1("C++ primer", 128.0, 20, 0.9);
52     print_total(cout, b1, 11);
53     print_total(cout, b1, 9);
54     print_total(cout, l1, 21);
55     print_total(cout, l1, 19);
56     system("pause");
57     return 0;
58 }
59
60 double print_total(ostream & os, const Quote &item, size_t t)
61 {
62     double ret = item.net_price(t);
63     os << "ISBN: " << item.isbn() << " # sold: " << t << " total due: " << ret << endl;
64     return ret;
65 }
66
67 double Bulk_quote::net_price(size_t n) const
68 {
69     if (n >= quantity)
70         return n * (1 - discount) * price;
71     else
72         return n * price;
73 }
74
75 double lim_discount::net_price(size_t n) const
76 {
77     if (n <= quantity)
78         return n * (1 - discount) * price;
79     else
80         return Quote::net_price(n);
81 }

练习15.17

1>f:\c++projicets\project1\project1\源.cpp(56): error C2259: “Disc_quote”: 不能实例化抽象类
1> f:\c++projicets\project1\project1\源.cpp(56): note: 由于下列成员:
1> f:\c++projicets\project1\project1\源.cpp(56): note: “double Disc_quote::net_price(std::size_t) const”: 是抽象的
1> f:\c++projicets\project1\project1\源.cpp(26): note: 参见“Disc_quote::net_price”的声明
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