add this function to your functions.php class and then add the filter to the result you need to have it.

even-odd for functions.php

function oddeven_post_class ( $classes ) {
		global $current_class;
		$classes[] = $current_class;
		$current_class = ($current_class == 'odd') ? 'even' : 'odd';
		return $classes;
}
add_filter ( 'post_class' , 'oddeven_post_class' );
global $current_class;
$current_class = 'odd';