How to get ID of parent category in WordPress

Some times you need to get ID of the parent category. Here is the code which will display the ID of parent category. this code will work fine with WordPress versions 1.5.1 and above.

 
	<?php
	if( is_category() ) {
	  $query_cat = get_query_var('cat');
	  $cat = get_category( $query_cat );
	  echo $cat->category_parent; // Display the ID
	}
	?>