I have written the following program
==========================
class derived
{
public:
int i;
void derived::f()
{
cout << "f is exe"<<endl;
}

derived()
{
cout << "hi"<<endl ;
}

~derived()
{
cout << "destroy me " << endl;
}

};

int main()
{

derived *pDerived1 = new derived ;
cout << pDerived1<<endl;
pDerived1 -> i =5;
cout << pDerived1 ->i <<endl;
delete pDerived1;
cout << pDerived1<<endl;
cout << pDerived1 ->i <<endl;
pDerived1 = NULL;
cout << pDerived1<<endl;
pDerived1->f();
cout << pDerived1<<endl;
return 0;
}

===============
output of program: Platform CC /Solaris
===============
hi
63380
5
destroy me
63380
5
0
f is exe
0
=================
My Questions:
=================
Why after deleting It is showing the same memory location ?
and how it is possible to access the method of the class after delete ?
I have explicitly assigned pDerived1 = NULL then also
class method f() is accessible how it is working ?

Please give me details.

I think that this is not official C++ behaviour, so you should not depend on it. This is what happens:

new allocates some memory for a new object, and returns a pointer to that memory. Delete de-allocates that memory, but the pointer is still pointing to the (de-allocated) memory location. Using that pointer results in undefined behaviour. In your case it just works, but you might get a segmentation fault on other platforms.

What happens if you call a method of an object, is that some executable code is executed, like a normal C function, and a pointer to the object itself is given to the nethod as an argument with the name "this". Your method f doesn't use this, or any member variables of the class, so in this case it doesn't matter for f() that the this-pointer points to de-allocated memory.