int popFirst() {
    int toBeReturned=0;
    if (!isEmpty()) {
        toBeReturned = first->val;
        temp = (node_t*) malloc (sizeof (node_t));
        temp = first->NEXT;
        if (first->NEXT == NULL) {
            first = last = NULL;
        }
        else {
            free(first);
            temp->PREV = NULL;
            first = temp;
        }
    }
    return toBeReturned;
}