void list_users(const User *curr) {
    // start at the curr user
    User *curr_user = (User *) curr;
    // keep going through the linked list till the end is reached
    while(curr_user != NULL){
        // THIS LINE BELOW IS A PROBLEM!
        printf(stdout, "%s\n", curr_user->name);
        //print_user(curr);
         curr_user = curr_user->next;
    }
}
/*
 * Print the usernames of all users in the list starting at curr.
 * Names should be printed to standard output, one per line.
 */