Cannot retrieve a value from a checkbox on validated php form
<p>I have never done any PHP or coding before, super newbie here. I have put together a form using bits and pieces of code I have found over the net. It is a validated form that displays success/error msgs once submitted.</p>

<p>I get successful msgs when submitted, however my checkbox gets displayed with a value "1" which I cannot change. My aim is to have the form post the values "Yes" for checked and "No" for unchecked.
Any help will be appreciated. 
Here is the code used:</p>

<p>HTML
</p>

<p>PHP


<pre><code>error_reporting(E_NOTICE);

function valid_email($str)
{
    return ( ! preg_match("/^([a-z0-9\+_\-]+)(\.[a-z0-9\+_\-]+)*@([a-z0-9\-]+\.)+[a-z]{2,6}$/ix", $str)) ? FALSE : TRUE;
}
if(isset($_POST['samples']));
if($_POST['your_name']!='' &amp;&amp; $_POST['company_name']!='' &amp;&amp; $_POST['referral']!=''  &amp;&amp; $_POST['e_mail']!='' &amp;&amp; valid_email($_POST['e_mail'])==TRUE &amp;&amp; strlen($_POST['message'])&gt;5)


{
    $to = 'test@testemail.com';
    $headers =  'From: '.$_POST['e_mail'].''. "\r\n" .
            'Reply-To: '.$_POST['e_mail'].'' . "\r\n" .
            'X-Mailer: PHP/' . phpversion();
    $subject = "Website Enquiry";
    $message = htmlspecialchars('Client Name: '.$_POST['your_name'] ."\r\n"
    .'Company Name: '.$_POST['company_name'] ."\r\n"
    .'Email: '.$_POST['e_mail'] . "\r\n" 
    .'Referral Source: '.$_POST['referral'] . "\r\n" 
    .'Require Samples: '.(isset($_POST['samples'])) . "\r\n"
    . 'Enquiry: '.$_POST['message']."\r\n");

    if(mail($to, $subject, $message, $headers))
    {
        echo 'Thank you '.$_POST['your_name'].'. Your message was sent and we will respond promptly';
    }
    else {
    echo 'Please make sure you filled all the required * fields, 
    and re-submit this form.';
}
</code></pre>
