verifying if checkbox is checked in php
<p>I want to verify if my checkbox is checked in php and if it is, i want to echo "Hello word".
Here is my html code :</p>

<pre><code>&lt;form class="checkclass"&gt;
&lt;input type="checkbox" name="checkbox1"&gt; 4K &lt;/input&gt;
&lt;/form&gt;
</code></pre>

<p>php :</p>

<pre><code> &lt;?php
if (isset($_POST['checkbox1'])) {
    echo "Hello world!";
}
?&gt;
</code></pre>

<p>But it doesn't work and i really don't know how to fix this.
Can someone please help me ?</p>