php calc

<!DOCTYPE html>
<html lang="de">
<head>
<meta charset="utf-8">
<title>dEn Cliqulatoz</title>
<h1>THe KLaCULATIOR</h1>
</head>
<body bgcolor="#FF00FF" background="http://bestanimations.com/Animals/Birds/Parrots/animated-parrot-gif-2.gif">
<form method="post" attribute="post" >
<p>First Value:<br/>
<input type="text" id="first" name="first"></p>
<p>Second Value:<br/>
<input type="text" id="second" name="second"></p>

<!--
<input type="radio" name="group1" id="add" value="add" checked="true"><p>+</p><br/>
<input type="radio" name="group1" id="subtract" value="subtract"><p>-</p><br/>
<input type="radio" name="group1" id="times" value="times"><p>x</p><br/>
<input type="radio" name="group1" id="divide" value="divide"><p>/</p><br/>
<p></p>
-->

<button type="submit" name="group1" id="add" value="add">+</button>
<button type="submit" name="group1" id="subtract" value="subtract">-</button>
<button type="submit" name="group1" id="times" value="times">*</button>
<button type="submit" name="group1" id="divide" value="divide">/</button>

<p>
answer
<p>

<?php
$first = $_POST['first'];
$second = $_POST['second'];
if($_POST['group1'] == 'add') {
echo $first + $second;
}
else if($_POST['group1'] == 'subtract') {
echo $first - $second;
}
else if($_POST['group1'] == 'times') {
echo $first * $second;
}
else if($_POST['group1'] == 'divide') {
echo $first / $second;
}
?>
</form>
</body>
</html>