int push_back(pos_t *head, int new_value) {
    pos_t *temp = head;

    while (temp->next != NULL) {
        temp = temp->next;
    }
    pos_t *temp1 = (pos_t *)malloc(sizeof(pos_t));
    temp1->data = new_value;
    temp1->next = NULL;
    temp = temp1;
}

if (temp1 == NULL) { return 1; }

int push_back(pos_t **headp, int new_value);

int push_back(pos_t **headp, int new_value) {
    pos_t *temp = *headp;
    pos_t *temp1 = malloc(sizeof(pos_t));
    if (temp1 == NULL) {   // allocation failure
        return 1;
    }
    temp1->data = new_value;
    temp1->next = NULL;

    if (temp == NULL) {      // empty list
        *headp = temp1;
    } else {
        while (temp->next != NULL) {
            temp = temp->next;
        }
        temp->next = temp1;  // append node to the end of the list
    }
    return 0;
}