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When you call delete BasePtr();, the destructor of the class which is pointed by BasePtr needs to be called. To acheive this, we need the destructor to be virtual.

Without Virtual, the delete BasePtr() will call the class of type BasePtr.

If destructor is not declared virtual in base class, then when you try to delete a derived class using base class pointer, the destructor of base class is called instead of the derived class destructor. Hence virtual destructor.

Just to add a note to vk..if we declare the base class destructor as virtual and if try to delete the base class pointer..
The order of execution of destructor in an inherited class during a clean up is like this.
1. Derived class destructor
2. Base class destructor

read chap 15 of bruce eckel book vol-1(Thinking in C++)

read chap 15 of bruce eckel book vol-1(Thinking in C++)

#include<iostream>
using namespace std;

class A{
public:
A(){
cout<<"in a \n";
}
virtual ~A(){
cout<<"out A"<<endl;
}
};

class b:public A{

public:
b(){
cout<<"in B\n"<<endl;
}
~b(){
cout<<"out b"<<endl;
}
};


int main(){
A *bc=new b();
// A *a=new A();

delete bc;
getchar();
}