026：编程填空：统计动物数量

标签：num int 编程 number Dog 026 Animal 填空 Cat

知识点1：static静态变量在类内声明，但必须在类外初始化

知识点2：构造函数不能是虚函数

知识点3：如果基类构造函数里所有参数有缺省值，那么派生类函数可以不为其初始化，基类会自行用缺省值初始化变量

知识点4：一个派生类对象消亡时，除了会调用该派生类的析构函数，还会调用基类的析构函数（先派生后基类）

i.

 1 #include <iostream>
 2 using namespace std;
 3 class Animal{
 4     public:
 5         static int number;
 6         Animal(int num = 1){Animal::number = Animal::number + num;}
 7         virtual ~Animal(){-- Animal::number;}
 8 }; 
 9 int Animal::number = 0;
10 
11 class Dog:public Animal{
12     public:
13         static int number;
14         Dog(int num = 1){
15             Dog::number = Dog::number + num;
16         }
17         ~Dog(){-- Dog::number;}
18 };
19 int Dog::number = 0;
20 
21 class Cat:public Animal{
22     public:
23         static int number;
24         Cat(int num = 1){
25             Cat::number = Cat::number + num;
26         }
27         ~Cat(){-- Cat::number;}
28 };
29 int Cat::number = 0;
30 void print() {
31     cout << Animal::number << " animals in the zoo, " << Dog::number << " of them are dogs, " << Cat::number << " of them are cats" << endl;
32 }
33 
34 int main() {
35     print();
36     Dog d1, d2;
37     Cat c1;
38     print();
39     Dog* d3 = new Dog();
40     Animal* c2 = new Cat;
41     Cat* c3 = new Cat;
42     print();
43     delete c3;
44     delete c2;
45     delete d3;
46     print();
47 }

ii.

 1 #include <iostream>
 2 using namespace std;
 3 class Animal{
 4     public:
 5         static int number;
 6         Animal(/*int num = 1*/){}
 7         virtual ~Animal(){-- Animal::number;}
 8 }; 
 9 int Animal::number = 0;
10 
11 class Dog:public Animal{
12     public:
13         static int number;
14         Dog(int num = 1){
15             Animal::number = Animal::number + num;
16             Dog::number = Dog::number + num;
17         }
18         ~Dog(){-- Dog::number;}
19 };
20 int Dog::number = 0;
21 
22 class Cat:public Animal{
23     public:
24         static int number;
25         Cat(int num = 1){
26             Animal::number = Animal::number + num;
27             Cat::number = Cat::number + num;
28         }
29         ~Cat(){-- Cat::number;}
30 };
31 int Cat::number = 0;
32 void print() {
33     cout << Animal::number << " animals in the zoo, " << Dog::number << " of them are dogs, " << Cat::number << " of them are cats" << endl;
34 }
35 
36 int main() {
37     print();
38     Dog d1, d2;
39     Cat c1;
40     print();
41     Dog* d3 = new Dog();
42     Animal* c2 = new Cat;
43     Cat* c3 = new Cat;
44     print();
45     delete c3;
46     delete c2;
47     delete d3;
48     print();
49 }

2个代码体现了知识点3

标签：num,int,编程,number,Dog,026,Animal,填空,Cat
From： https://www.cnblogs.com/balabalabubalabala/p/16647496.html