array_key_exists
<p>I'm implementing some affiliate tracking to my site. The affiliate network has asked that I hide the telephone number on the site.</p>

<p>When an affiliate clicks on a link to my site, any of the site URLs will be appended wth something like /?source=affiliate&amp;siteid=XXXX for example; mydomain.com/?source=affiliate&amp;siteid=XXXX</p>

<p>I've been trying to do this to hide the telephone number;</p>

<pre><code>&lt;?php
 if (!array_key_exists('affiliate', $_GET)){
  //Show telephone number
  echo "&lt;li&gt;+44 (0)1234 567891&lt;/li&gt;";
 }
?&gt;
</code></pre>

<p>However, this doesn't seem to be working. Ideally I need to show the number by default, but if the URL contains the affilaite part of the url, then the telephone number should be hidden.</p>
