int create_user(const char *name, User **user_ptr_add) {
    
    // Check if name is too long
    if (strlen(name) >= MAX_NAME){
    }

    User *new_user = (User*) malloc(sizeof(User));
    strncpy(new_user->name, name, MAX_NAME);

    for (int i = 0; i < MAX_FRIENDS; i ++){
        new_user->friends[i] = NULL;
    }

    new_user->first_post = NULL;
    new_user->next = NULL;


    // If user_ptr_add is empty, add the new user.
    if (*user_ptr_add == NULL){
        // *user_ptr_add = (User*) malloc(sizeof(User));
        *user_ptr_add = new_user;
        return 0;
    }
    
    // If not empty, traverse the list.
    User *curr = *user_ptr_add;

    while (curr->next != NULL){
        if (curr->name == name){
            return 1;
        }

        curr = curr->next;
    }

    curr->next = (User*) malloc(sizeof(User*));
    (curr->next) = new_user;

    return 0;
}
Insert a User into the end of the linked list *user_ptr_add