/*
 * Print the usernames of all users in the list starting at curr.
 * Names should be printed to standard output, one per line.
 */
void list_users(const User *curr) {

    // loop through linked list
    User *curr = curr;
    while (curr != NULL) {
        printf("%s\n", curr->name);
        curr = curr->next;
    }
}
print all linked list nodes