my $i=0;
my $mod=0;
my $class;

while ($pointer = $sth->fetchrow_hashref)			{
  $mod=($i % 2);
  if($mod == 0)  {
                    $class="even";
                  }else {
                        $class="odd";
                         }
                          $i++;
       ...more stuff goes here....
}