If you need to arrange items left and while performing a {foreach...} loop, you can determine the module of the index property of each item during the iteration.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | {foreach $pages.data as $page}
<div class="{if $page@index%2 == 1}right{else}left{/if}">
{$page.post_title}
</div>
{/foreach}
{*
index 0%2 = 0
index 1%2 = 1
index 2%2 = 0
index 3%2 = 1
index 4%2 = 0
index 5%2 = 1
*} |
{foreach $pages.data as $page}
<div class="{if $page@index%2 == 1}right{else}left{/if}">
{$page.post_title}
</div>
{/foreach}
{*
index 0%2 = 0
index 1%2 = 1
index 2%2 = 0
index 3%2 = 1
index 4%2 = 0
index 5%2 = 1
*}