织梦有缩略图显示,没有显示随机指定图片的办法

[field:array runphp='yes']
@me = (strpos(@me['litpic'],'defaultpic') ? "
<a class='focus' href='{@me['arcurl']}'><img src='/images/default/".mt_rand(1,30).".jpg' class='thumb' /></a>" : "
<a class='focus' href='{@me['arcurl']}'><img src='{@me['litpic']}' class='thumb'/></a>"); 
[/field:array]

{dede:field name='array' runphp='yes'}
@me = (strpos(@me['litpic'],'defaultpic') ? "
 <img src='/images/default/".mt_rand(1,30).".jpg' alt='{@me['title']}' />" : "
<img src='{@me['litpic']}' alt='{@me['title']}' />"); 
{/dede:field}