automatically add category to custom post type

Hi,

I am trying to automatically set a category per custom post type. I already created categories CAT1, CAT2, CAT3 and custom post types CPT1, CPT2, CPT3. Now I would like to assign:

CAT1 to CPT1
CAT2 to CPT2
CAT3 to CPT3

I can get this to work in my functions.php with what I have so far but only for one category and one custom post type. I tried to change this into a condition so I can assign each category to each of the custom post types, but I am missing something and I can’t get the conditions to work.

Thank you already for your help ??

function wpc_update_post_terms( $post_id )
{
	if ( $parent = wp_is_post_revision( $post_id ) )
        $post_id = $parent;
    $post = get_post( $post_id );
    if ( $post->post_type != 'CPT1' )
        return;
 //adding the category
    $categories = wp_get_post_categories( $post_id );
    $newcat1    = get_term_by( 'slug', 'CAT1', 'category' );
    array_push( $categories, $newcat1->term_id );
    wp_set_post_categories( $post_id, $categories );
}
add_action( 'wp_insert_post', 'wpc_update_post_terms' );