04737_C++程序设计_第8章_多态性和虚函数

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 const double PI = 3.14159;
 6 
 7 class Point
 8 {
 9 private:
10     double x, y;
11 public:
12     Point(double i, double j)
13     {
14         x = i;
15         y = j;
16     }
17     virtual double area()
18     {
19         return 0;
20     }
21 };
22 
23 class Circle :public Point
24 {
25 private:
26     double radius;
27 public:
28     Circle(double a, double b, double r) :Point(a, b)
29     {
30         radius = r;
31     }
32     double area()
33     {
34         return PI*radius*radius;
35     }
36 };
37 
38 void display(Point *p)
39 {
40     cout << p->area() << endl;
41 }
42 
43 void display(Point&a)
44 {
45     cout << a.area() << endl;
46 }
47 
48 void main()
49 {
50     Point a(1.5, 6.7);
51     Circle c(1.5, 6.7, 2.5);
52 
53     Point *p = &c;
54     Point &rc = c;
55 
56     display(a);
57     display(p);
58     display(rc);
59 
60     system("pause");
61 };

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 class A
 6 {
 7 public:
 8     A()
 9     {
10 
11     }
12     virtual void func()
13     {
14         cout << "Constructing A" << endl;
15     }
16     ~A()
17     {
18 
19     }
20     virtual void fund()
21     {
22         cout << "Destructor A" << endl;
23     }
24 };
25 
26 class B :public A
27 {
28 public:
29     B()
30     {
31         func();
32     }
33     void fun()
34     {
35         cout << "Come here and go...";
36         func();
37     }
38     ~B()
39     {
40         fund();
41     }
42 };
43 
44 class C :public B
45 {
46 public:
47     C()
48     {
49 
50     }
51     void func()
52     {
53         cout << "Class C" << endl;
54     }
55     ~C()
56     {
57         fund();
58     }
59     void fund()
60     {
61         cout << "Destructor C" << endl;
62     }
63 };
64 
65 void main()
66 {
67     C c;
68     c.fun();
69 
70     system("pause");
71 };

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 class A
 6 {
 7 public:
 8     virtual void f()
 9     {
10         cout << "Call A" << endl;
11     }
12 };
13 
14 class B
15 {
16 public:
17     virtual void f()
18     {
19         cout << "Call B" << endl;//必须使用virtual声明
20     }
21 };
22 
23 class C :public A, public B
24 {
25 public:
26     void f()//可以省略关键字virtual
27     {
28         cout << "Call C" << endl;
29     }
30 };
31 
32 void main()
33 {
34     A *pa;
35     B *pb;
36     C *pc, c;
37 
38     pa = &c;
39     pb = &c;
40     pc = &c;
41 
42     pa->f();//输出Call C
43     pb->f();//输出Call C
44     pc->f();//输出Call C
45 
46     system("pause");
47 };