Can someone please help me in debug that code

Question

#include<iostream>
using namespace std;
class A
{
public:
virtual void show()
{
cout<<"parent class is A"<<endl;
}
};
class B: public A
{
public:
void show()
{
cout<<"child class B is"<<endl;
}
};
class C: public A
{
void show()
{
cout<<"child class C is"<<endl;
}
};
int main()
{
A obj1;
B obj2;
C obj3;
ptr=&obj1;
ptr->show();
ptr=&obj2;
ptr->show();
ptr=&obj3;
ptr->show();
return 0;
}

Answer 1

I guess "A *ptr" Is missing