#include<iostream>
using namespace std;
class A
{
      public:
     virtual int get(){return 1;} //难道不对吗这里？
};
class B:public A
{
      public:
      int get(){return 2;}
};
int main()
{
    while(1)
    {
    cout<<"1:父类2:子类3:退出："<<endl;
    int choice;
    cin>>choice;
    A*p;
    bool quit =false;
    switch(1)
    {
             case 1:p=new A;
             break;
             case 2:p=new B;
             break;
             case 3:quit=true;
             break;
             default:
                     cout<<"请输入1，2，3"<<endl;
             break;
    }
    if(quit==true)
    {
                  break;
    }
    cout<<p->get()<<endl;
}
system("pause");
return 0;
}

C++、面向对象

switch(1)？？ switch(choice)

#include<iostream>
using namespace std;
class A
{
      public:
     virtual int get(){return 1;} //It's ok here:-)
};
class B:public A
{
      public:
      int get(){return 2;}
};
int main()
{
    while(1)
    {
    cout<<"1:父类2:子类3:退出："<<endl;
    int choice;
    cin>>choice;
    A *p;
    bool quit =false;
    switch(choice)  //error writing in your code!
    {
             case 1:p=new A;
             break;
             case 2:p=new B;
             break;
             case 3:quit=true;
             break;
             default:
                    p=NULL;cout<<"请输入1，2，3"<<endl; //here is a bug in your design, pointer p is not evaluated!
             break;
    }
    if(quit==true)
    {
                  break;
    }
    if(NULL!=p)  //you'd better check p here when you using it
    {

        cout<<"the return value is: "<<p->get()<<endl;
    }

    else
    {
        cout<<"p is not evaluated!"<<endl;
    }
}
system("pause");
return 0;
} 

[ 本帖最后由 Pirelo 于 2011-5-24 19:20 编辑 ]

我写错了，不好意思哈

好强