// polymo.cpp -- CopyWrong by tsaiwn@csie.nctu.edu.tw
#include <iostream.h>
class Shape{
   public:
    virtual    // 把這列去掉再 run 看看, 去掉就沒 polymorphism
       void draw(  )  { cout << "drawing\n"; }
};
class Line: public Shape{
   public:
      void draw( ) { cout << "draw a line\n"; }
};
class Circle: public Shape{
   public:
      void draw( ) { cout << "here is a circle\n"; }
};
int main( ) {
   Circle * ppp;
   Shape * fig[9];   // base class的指標可指向衍生出的object
  // ppp = new Shape( );   // error! 
   ppp = (Circle *)new Shape( );    /* cast */
   ppp -> draw( );
   ppp = (Circle *)new Line( );      ppp -> draw( );
   ppp = new Circle( );       ppp -> draw( );
   cout << "======" << endl;
   fig[0] = new Line( );
   fig[1] = new Circle( );
   fig[2] = new Circle( );
   fig[3] = new Line( );   fig[4] = new Circle( );
   for(int k=0; k<5; k++){
        fig[k] -> draw( );
   }
}