how to change path wordpress plugin directory code example

Example 1: how to get plugin directory path in wordpress

if ( is_admin() ) {
    include_once( plugin_dir_path( __FILE__ ) . 'includes/admin-functions.php' );
} else {
    include_once( plugin_dir_path( __FILE__ ) . 'includes/front-end-functions.php' );
}

Example 2: how to get plugin directory path in wordpress

define( 'MY_PLUGIN_PATH', plugin_dir_path( __FILE__ ) );
include( MY_PLUGIN_PATH . 'includes/admin-page.php');
include( MY_PLUGIN_PATH . 'includes/classes.php');
// etc.