C.....Shufling values of linked list

Question

I am writing a war cards game. I need to shufle first few elements of players hand (linked list). That`s what i have:

void tasowanie(llist_t** head, int warsize) {
    llist_t** temp = head;
    Card_t temp_card;
    int random;

    while (warsize > 0) {
        random = rand() % warsize;
        for (int j = 0; j < random; j++)
            if ((*temp)!=NULL && (*temp)->next != NULL)
                *temp = (*temp)->next;
        temp_card = (*head)->card;
        (*head)->card = (*temp)->card;
        (*temp)->card = temp_card;
        *head = (*head)->next;
        *temp = *head;
        warsize--;
    }
}

The problem is that I am losing elements of this list. I was thinking about puting these elements into array, then shufling it and puting it back to the list, although I imagine there has to be more elegant solution.

Answer 1

You should not be writing to *temp, as this is a pointer to the real list next pointer.

The same applies to moving head: unless you intend to update the list you should not be touching *head.

Instead, when you want to update temp you should set it with temp = &((*temp)->next), and reset with temp=head.

void tasowanie(llist_t** head, int warsize) {
    llist_t** temp = head;
    Card_t temp_card;
    int random;

    while (warsize > 0) {
        random = rand() % warsize;
        for (int j = 0; j < random; j++)
            if ((*temp)!=NULL && (*temp)->next != NULL)
                temp = &((*temp)->next);
        temp_card = (*head)->card;
        (*head)->card = (*temp)->card;
        (*temp)->card = temp_card;
        head = &((*head)->next);
        temp = head;
        warsize--;
    }
}