Virtual Function in c++

/* Program by Arun Anoop M */

#include<iostream.h>
#include<conio.h>
class B
{
protected:
int a,b;
public:
virtual void show()
{
cout<<"Arithmetic Operations";
cout<<"Div="<<a/b;
}
void get()
{
cout<<"Enter 2 nos:";
cin>>a>>b;
}
};
class D1:public B
{
/*void get()
{
cout<<"Enter 2nos:";
cin>>a>>b;
} */

void show()
{
cout<<"ADD="<<a+b;
}
};
class D2:public B
{
void show()
{
cout<<"Subst="<<a-b;
cout<<"Mul="<<a*b;
}
};

void main()
{
B *p1;
B base1;
p1=&base1;
p1->get();
p1->show();

D1 der1;
p1=&der1;
p1->get();
p1->show();

D2 der2;
p1=&der2;
p1->get();
p1->show();

getch();
}