void pop(start)
    struct node *start;
{
    if(start == NULL) {
        printf("The list is empty!\n");
        return;
    }
    struct node *temp = start;
    start = temp->next;
    temp->next = start->prev = NULL;
    free(temp);
    return; # or maybe we can return the element popped before freeing temp or whatever.
}