I'm trying to increment the row number but each row has id="1". What am I doing wrong?

$rowNum = 1;

@$content .= "<tr class=\"sortable\" id=\"' . ++$rowNum . '\" bgcolor=\"$col\">\n<td>$a1[ItemName]</td><td>$a1[ItemNum]</td><td>$itemprice</td><td align=\"center\"><a href=\"re.php?opt4&id=$a1[ItemID]\" title=\"Remove\">X</a></td></tr>\n";

Disregard, this works: id=\"" . ++$rowNum . "\"