if(isset($_POST['username'])) $username = $_POST['username'];
if(isset($_POST['password'])) $password = $_POST['password'];
if(isset($_POST['action'])) $action = $_POST['action'];

if(isset($action)) {
	switch($action) {
		case 'ADD':
			$file = 'testdata.txt';
			$file = fopen($file, 'a') or die('cant open file');
			fwrite($file, $username . ' ' . $password . chr(13));
			fclose($file);
			return '111';
			break;

		default:
			echo '<p>' . $action . '</p>';
			echo '<p>' . $username . '</p>';
			echo '<p>' . $password . '</p>';
			break;
	}
}