Delete multiples for prime sieve on linked list

example.c

node* Deletemultiples(node* head, int k)
{
    node* temp = head, *old = head, *todelete;
    if (head == NULL)
        return NULL;

    while (temp!=NULL) {
        if (temp->data % k ==0 && temp->data != k) {
            todelete = temp;

            if (temp == head)
                head = temp->next;
            else
                old->next = temp->next;
            
            temp = temp->next;

            free(todelete);
        }
        else {
            old = temp;
            temp = temp->next;
        }
    }
    return head;
}