How is `if (!integer) {}` evaluated?
<p>I came across this code in a php database class:</p>

<pre><code>if( !$this-&gt;_Link_ID )
</code></pre>

<p><code>Link_ID</code> is an integer.</p>

<p>So does this code just check if <code>Link_ID</code> is not <code>0</code>?</p>

<p>I know from experience that if a variable is type Boolean, you can just test the var like</p>

<pre><code>$myBoolean = true;
if ($myBoolean){
    // code
}
</code></pre>

<p>I didn't realise this can be done for integers.</p>

<p>So how is <code>if( !$this-&gt;_Link_ID )</code> evaluated?</p>
