022：看上去像多态

#include <iostream>
using namespace std;
class B { 
    private: 
        int nBVal; 
    public: 
        void Print() 
        { cout << "nBVal="<< nBVal << endl; } 
        void Fun() 
        {cout << "B::Fun" << endl; } 
        B ( int n ) { nBVal = n;} 
};
class D:public B{
14     private:
15         int nDVal;
16     public:
17         void Print() { 
18            B::Print();
19            cout << "nDVal="<< nDVal << endl; 
20         } 
21         void Fun() 
22         {cout << "D::Fun" << endl; } 
23         D ( int n ):B(n * 3) { nDVal = n;} //一个派生类对象可以看作是一个基类对象，是对其扩充，所以记得 ！！派生类对象要对基类对象成员进行初始化！！！（D ( int n ):B(n * 3)） 
24 };
int main() { 
    B * pb; D * pd; 
    D d(4); d.Fun(); 
    pb = new B(2); pd = new D(8); 
    pb -> Fun(); pd->Fun(); 
    pb->Print (); pd->Print (); 
    pb = & d; pb->Fun(); 
    pb->Print(); 
    return 0;
}