In this code if we can access show() of class y with its own object then why are we making show as a virtual function in class x?

class Dog
{
public:
    virtual void bark() =0;
};

class Beagle: public Dog
{
public:
    virtual void bark() { cout << "bark!"; }
};

class GreatDane: public Dog
{
public:
    virtual void bark() { cout << "BARK!"; }
};

class x
{
public:
  void  DoJob()
  {
    // do anything and final:
    show();
  }

  virtual void show()
  {
    cout<<"Base show()"<<endl;
  }
};
 
class y:public x
{
public:
  void show()
  {
    cout<<"Class y show()";
  }
};
 
int main()
{
  y ob1;
  ob1.DoJob();
  getch();
  return 0;
}