I was provided this code for a Contact Form where the Agree To Terms have to checked in a checkbox in order to submit.
However, I tested and can proceed without checking the box.
Can you help me figure out how to make it mandatory to check the box in order to submit?

Thanks

Code:
<?php
$mailto     = 'email@email.com';
$mailsubj   = "Contact Form submission";$mailhead   = "From:CForm\n";
$mailbody   = "--- Contact form results ---\n";
foreach($_REQUEST as $key => $value)    
{   
 if($key != 'PHPSESSID')        
{        
$mailbody .= $key.": ".$value."\n";        
}    
}
$continue = true;if(isset($_POST['ans']) && $_POST['ans']!='hot')
{  
echo 'Wrong answer!';  
$continue = false;
}
// if the check box is not checked it will not appear in the $_POST values, it's better to use isset rather than empty
if(isset($_POST['agree']))
{  
echo "If you agree with the terms, check the Agree check box";  
$continue = false;
}
if($continue)
{  
$mailbody .= date('Y-m-d H:i:s',strtotime("now"));  
mail($mailto, $mailsubj, $mailbody, $mailhead); 
echo "<h2>Thanks!</h2>";  
//print_r($_REQUEST);
}
?>