读一段程序

//test.cpp
#include <iostream.h>
#include "cat.h"
//忘记为静态类成员初始化将导致编译错误
int Cat::HowManyCats = 0;
void main()
{
      const int MaxCats = 5;
      Cat * CatHouse[MaxCats];
     
      for(int i=0; i<MaxCats; i++)
           CatHouse[i] = new Cat(i);
          
      for( i=0; i<MaxCats; i++)
      {
           cout << "There are ";
           cout << Cat::HowManyCats;
           cout << " cats left!\t" ;
          
           cout << "Deleting the one which is ";
           cout << CatHouse[i] -> GetAge();
           cout << " years old." << endl;
          
           delete CatHouse[i];
           CatHouse[i] = 0;
      }
}
//cat.h
#include <iostream.h>
class Cat
{
      public:
           Cat(int age):itsAge(age){HowManyCats++;}
           virtual ~Cat(){HowManyCats--;}
          
           virtual int GetAge()const {return itsAge;}
           virtual void SetAge(int age) { itsAge = age;}
          
           static int HowManyCats; //注意1：此处为公有
           //注意2：静态数据成员的声明处，不能初始化
          
      private:
           int itsAge;
};