expression must be a modifiable lvalue
for new_user->friends = { NULL };
int create_user(const char *name, User **user_ptr_add) {
    if (strlen(name) >= MAX_NAME){
        // if name is too long
        return 2;
    }

    // Create User
    User *new_user = (User*) malloc(sizeof(User));
    if (new_user == NULL) {
        free(new_user);
        return -1; // failed to allocate memory
    }
    if (strcpy(new_user->name, name) == NULL) {
        free(new_user);
    }
    
    new_user->profile_pic[0] = '\0';
    new_user->first_post = NULL;
    new_user->friends = { NULL };
    new_user->next = NULL;

    if (*user_ptr_add == NULL) {
        // If 0 users exists in the system
        *user_ptr_add = new_user;
        return 0;
    }

    if (find_user(name, *user_ptr_add) != NULL) {
        // If a user by this name already exists in this list
        return 1;
    }

    User *tail = *user_ptr_add;
    while (tail->next != NULL) {
        tail = tail->next;
    }
    tail->next = new_user;

    return 0;
}