int create_user(const char *name, User **user_ptr_add) {
    // ptr is pointer to a pointer to a struct
    // we are basically creating a new node in a linked list
    // to create a new node, we need the node that follows it
    // structs are not passed to functions in the ame way as arrays; we don't pass a pointer by default
    if(strlen(name) > (MAX_NAME + 1)) {return 2;} //stlen does not consider null terminator
    //Now, let's check if the name already exists: let's travense through the
    // linked list and check for the name of every other user:
    User* curr = *user_ptr_add;
    while (curr->next!= NULL)
    {
        if(curr->name == name){return 1;}
        curr = curr->next;
    }
    
    User* new_user = malloc(sizeof(User)); //allocate space for new user
    strcpy((*new_user).name, name);
    curr->next = new_user;

    return 0;
}
create_user should crreate a new user with the given name.  Insert it at the tail of the list of users whose head is pointed to by *user_ptr_add.