insert.c

/**
 * Tries to insert a number into list.
 */
void insert(void)
{
    // try to instantiate node for number
    node* newptr = malloc(sizeof(node));
    if (newptr == NULL)
    {
        return;
    }

    // initialize node
    printf("Number to insert: ");
    newptr->n = GetInt();
    newptr->next = NULL;

    // check for empty list
    if (first == NULL)
    {
        first = newptr;
    }

    // else check if number belongs at list's head
    else if (newptr->n < first->n)
    {
        newptr->next = first;
        first = newptr;
    }

    // else try to insert number in middle or tail
    else
    {
        node* predptr = first;
        while (true)
        {
            // avoid duplicates
            if (predptr->n == newptr->n)
            {
                free(newptr);
                break;
            }

            // check for insertion at tail
            else if (predptr->next == NULL)
            {
                predptr->next = newptr;
                break;
            }

            // check for insertion in middle
            else if (predptr->next->n > newptr->n)
            {
                newptr->next = predptr->next;
                predptr->next = newptr;
                break;
            }

            // update pointer
            predptr = predptr->next;
        }
    }

    // traverse list
    traverse();
}