Split foreach code based on even/odd - html

Question

I currently use a code to display some content in my Magento shop.
But now I want to split the loaded content based on even/odd into two different divs.
My current code is displayed below.
How can I split the code based on even/odd so that I get to <div class="block-specs">.
I want a div <div class="block-specs odd"> and <div class="block-specs even">
How can I achieve that?
Current code:
<?php if($_additionalgroup = $this->getAdditionalData()): ?>
<section id="additional">
<div class="box-collateral box-additional">
<h2><?php echo $this->__('Additional Information') ?></h2>
<?php $i=0; foreach ($_additionalgroup as $_additional): $i++; ?>
<div class="block-specs-<?php echo $i?>">
<h3 class="specs-<?php echo $i?>"><?php echo $this->__( $_additional['title'] )?></h3>
<table class="data-table specs-<?php echo $i?>" id="product-attribute-specs-table-<?php echo $i?>">
<col width="25%" />
<col />
<tbody>
<?php foreach ($_additional['items'] as $_data): ?>
<?php $_attribute = $_product->getResource()->getAttribute($_data['code']);
if (!is_null($_product->getData($_attribute->getAttributeCode())) && ((string)$_attribute->getFrontend()->getValue($_product) != '')) { ?>
<tr>
<th class="label"><?php echo $this->htmlEscape($this->__($_data['label'])) ?></th>
<td class="data"><?php echo $_helper->productAttribute($_product, $_data['value'], $_data['code']) ?></td>
</tr>
<?php } ?>
<?php endforeach; ?>
</tbody>
</table>
</div>
<script type="text/javascript">decorateTable('product-attribute-specs-table-<?php echo $i?>')</script>
<?php endforeach; ?>
</div>
</section>
<?php endif;?>

Answer 1

Check if the index is evenly divisable by 2 with '%' this returns the remainder after dividing (0 if even).
<?php foreach ($_additionalgroup as $i => $_additional):
// if evenly divisable by 2, it is even
$oddEven =($i % 2) ? 'odd':'even';
?>
<div class="block-specs-<?php echo $oddEven; ?>">