字符串比较不起作用

I am trying to change the output on something when a category ID equals a specific number. For some reason this always returns false. What am I missing?

<?php 
$ad_id = '#_CATEGORYID';
$id = 55;

if ($ad_id === $id ) {
    echo 'true';
} else {
    echo 'false';
}
?>

EDIT Sorry should have clarified, #_CATEGORYID is a shortcode from another application that returns integers. When echo $ad_id the value returned is 55.

It sounds to me like you may need to eval your third-party markup before the comparison.

<?php  
eval("\$ad_id = '#_CATEGORYID'"); 
$id = "55"; 

if ($ad_id === $id ) { 
    echo 'true'; 
} else { 
    echo 'false'; 
} 
?>