Question

I got the code from wikipedia for linked list ( http://en.wikipedia.org/wiki/Linked_list ).

But it prints the result in reverse order (5 4 3 2 1 ). How to make this to print from beginning ( 1 2 3 4 5).

Answer 1

Looking at the following example:

/****************************************************************/
/*  Function: Add an element to our list                        */
/*                                                              */
/*   Parameters: **p is the node that we wish to insert at.     */
/*               if the node is the null insert it at the beginning    */
/*               Other wise put it in the next space                   */


LLIST *list_add(LLIST **p, int i)
{
    if (p == NULL)           /*checks to see if the pointer points somewhere in space*/
        return NULL;

    LLIST *n = malloc(sizeof(LLIST));   /* creates a new node of the correct data size */
    if (n == NULL)
        return NULL;

    n->next = *p; /* the previous element (*p) now becomes the "next" element */
    *p = n;       /* add new empty element to the front (head) of the list */
    n->data = i;

    return *p;
}

Elements are being added to the beginning of the linked list when you call list_add. This is for efficiency reasons; you don’t have to transverse the entire linked list to insert an element (which you would have to do if you wanted to append).

To print in reverse, you can use recursion, build your own stack (which is the blind man’s recursion), or recreate the list in reverse. A recursive version:

void list_print_reverse(LLIST *n)
{
    if (n == NULL)
    {
        printf("list is empty\n");
        return;
    }

    if (n->next != NULL)
    {
        list_print_reverse(n->next);
    }

    printf("print %p %p %d\n", n, n->next, n->data);
}