C++的类(1)

 1 #ifndef STOCK00_H_  //ifndef防止双重定义 
 2 #define STOCK00_H_
 3 
 4 #include <string>
 5 
 6 class Stock //Stock即新类类型名 
 7 {
 8     private:  //使用该类的程序必须通过public成员函数（或友元函数，见chap11）才能访问private部分 
 9         std::string company;
10         long shares;  //股票数量 
11         double share_val;  //股票价格 
12         double total_val;  //股票总价 
13         void set_tot() {total_val=shares*share_val;}
14     public:  //使用该类的程序皆可直接访问public部分 
15         void acquire(const std::string & co,long n,double pr);
16         void buy(long num,double price);
17         void sell(long num,double price);
18         void update(double price);
19         void show();
20 };  //别忘了class花括号后有";"
21 
22 #endif
23 
24 /*还有第三种访问控制关键字protected，见后续chap13*/ 

 1 /***类成员函数的实现***/
 2 /*类成员函数头使用作用域运算符解析(::)来标识归属*/
 3 /*如update()成员函数的函数头：void Stock::update(double price)，标识符update()具有类作用域*/ 
 4 /*这种表示方法意味着可以将另一个累的成员函数命名为同名的update()*/
 5 /*与update()同属一类的其他成员函数可以不经(::)访问它，在类之外使用update()则需要其他措施(待续)*/
 6 /***类的实现***/
 7 
 8 #include <iostream>
 9 #include "stock.h"
10 
11 /*aquire管理对某公司股票的首次购买*/ 
12 void Stock::acquire(const std::string & co,long n,double pr)  
13 {
14     company=co;
15     if(n<0)
16     {
17         std::cout<<"Number of shares can‘t be negative,"
18                  <<company<<"shares set to 0.\n";
19         shares=0;
20     }
21     else
22         shares=n;
23     share_val=pr;
24     set_tot();
25 } 
26 
27 /*buy和sell管理增加和减少持有的股票*/
28 void Stock::buy(long num,double price) 
29 {
30     if(num<0)
31     {
32         std::cout<<"Number of shares perchased can‘t be negative,"
33                  <<"Transaction is aborted.\n";
34     }
35     else
36     {
37         shares+=num;
38         share_val=price;
39         set_tot();
40     }
41 }
42 
43 /*sell管理售出股票*/
44 void Stock::sell(long num,double price)
45 {
46     using std::cout;
47     if(num<0)
48     {
49         cout<<"Number of shares sold can‘t be negative."
50             <<"Transaction is aborted.\n";
51     }
52     else if(num>shares)
53         cout<<"You can‘t sell more than you have."
54             <<"Transaction is aborted.\n"; 
55     else
56     {
57         shares-=num;
58         share_val=price;
59         set_tot();
60     }
61 }
62 
63 /**/ 
64 void Stock::update(double price)
65 {
66     share_val=price;
67     set_tot();
68 }
69 
70 /**/
71 void Stock::show()
72 {
73     std::cout<<"Company:"<<company
74              <<" Shares:"<<shares<<‘\n‘
75              <<"Share Price:$"<<share_val
76              <<" Total Worth:$"<<total_val<<‘\n‘;
77 }
78 

 1 #include <iostream>
 2 #include "stock.h"
 3 int main()
 4 {
 5     Stock mc;
 6     mc.acquire("NanoSmart",20,12.50);
 7     mc.show();
 8     mc.buy(15,18.125);
 9     mc.show();
10     mc.sell(400,20.00);
11     mc.show();
12     mc.buy(300000,40.125);
13     mc.show();
14     mc.sell(300000,0.125);
15     mc.show();
16     return 0;
17 }