虚函数与多态性

#include<iostream.h>
class shape
{public:
  int a;
  shape(int t)
  {
      a=t;
  }
   virtual void area()
   {
      cout<<"shape\n";
  }
};
class circle: public shape
{
 public:
  void  area();
  circle(int x):shape(x){}
};
void circle::area()
{
    cout<<"\ncircle\n";
}

void f(shape &h)
{h.area();
}
void main()
{
 shape objs(1);
 f(objs);
 cout<<objs.a;
 circle objc(2);
 f(objc);
 cout<<objc.a<<endl;
}