Question:
Modify our Doubly Linked List code to include following index (rank) based access operations
int RetrieveAt(int index)
void DeleteAt(int index)
void Swap(int index, int index)
index starts at 0 (just like array''s subscript)
If the index is out of bound, RetrieveAt returns -999, DeleteAt does nothing, do nothing in Swap.
Write your own testing program to test the modified class