#include <stdio.h>

typedef double ListData;

struct List
{
    ListData data;
    List * prev;
    List * next;
};

List * insertAfter (List * element, ListData value){
    List * newElement = new List;
    newElement -> data = value;
    newElement -> prev = element;
    if (element != 0){
	newElement -> next = element -> next;
	element -> next = newElement;
	if (newElement -> next)
	    newElement -> next -> prev = newElement;
    }
    else
	 newElement->next = 0;
    return newElement;
}

List * removeElement (List * element){
    if (!element) return 0;
    List * next = element -> next;
    if (element -> prev)
	element -> prev -> next = element -> next;
    if (element -> next)
	element -> next -> prev = element -> prev;
    delete element;
    return next;
}

void removeList (List * head){
    while (head) 
	head = removeElement (head);
}

List * next (List * elem){
    if (elem == 0) return 0;
    return elem -> next;
}

List * prev (List * elem){
    if (elem == 0) return 0;
    return elem -> prev;
}

List * element (List * head, unsigned index){
    List * result = head;
    for (;index > 0; --index) 
    result = next (result);
    return result;
}


void printList (List * head){
    List *elem;
    printf ("list\n");
    for (elem = head; elem; elem = next(elem))
	printf ("\tdata: %lg ptr: %p prev: %p next: %p\n", elem->data, elem, elem->prev, elem->next);
    printf ("end_list\n");
}

int main (void){
    List * head = 0, * tail = 0;
    head = insertAfter (0, 1);
    insertAfter (head, 2);
    insertAfter (head, 3);
    printList (head);
    element (head, 1) -> data = 10;
    printList (head);
    removeElement (head -> next);
    printList (head);
    removeList (head);
    return 0;
}