Hide menu items from customers?

(I do not speak English well)…

I use the following code but it is not good.
What is wrong?

<?php
if ( is_user_logged_in() ) {
    wp_nav_menu(array('theme_location' => 'main', 'menu_id' => 'menu'));
} else {
    wp_nav_menu(array('theme_location' => 'main', 'menu_id' => 'visitor'));
};
?>

[Please post code or markup snippets between backticks or use the code button.]

I want to watch a member of each menu item the customer is not all.

solvable??