/**
* When /^I convert it to Kelvin$/
**/
public function stepIConvertItToKelvin()
{
$this->aGlobals['kelvin'] = kelvinate($this->aGlobals['centigrade']);
}
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Kelvinator</title>
</head>
<body>
<h1>Kelvinator</h1>
<?php
if (array_key_exists("centigrade", $_GET)) {
require "kelvinator.php";
$centigrade = $_GET["centigrade"];
$kelvin = kelvinate($centigrade);
?>
<p><?php
echo $centigrade;
?>
°C is <span id="kelvin"><?php
echo $kelvin;
?>
°K</span></p>
<?php
} else {
?>
<form action="index.php" method="GET">
<input name="centigrade" type="text">
<label for="centigrade">°C</label>
<input type="submit" value="Kelvinate!">
</form>
<?php