各位大哥，帮我看个题！！！谢谢啦

#include <iostream>
#include <string>
using namespace std;
class A
{
   public:
     A(int i=0){a=i;}
     virtual void print()
        { cout<<a<<endl;}
     virtual ~A()
        { cout<<"A free!"<<endl;}
    protected:
      int a;
};
class B: public A
{
   public:
      B(char *,int);
      ~B( ){
        cout<<"B free!"<<endl;
        delete [ ]message;}
      virtual void print( );
    private:
       char *message;
       int len;
};
   B::B(char *s,int i):A(i) {
     len=strlen(s)+1;
     message=new char[len];
     strcpy(message,s); }
   void B::print( ) {
      A::print( );
      cout<<message<<endl; }
void main( )
   {   A *pa=new B("this",10);
       pa->print( );
       delete pa; }
运行结果：10
          this
          B free！
          A free！
         Press any key to continue