How to Use Cookies in PHP (Basic)

<?php
if (!isset($_POST['email'])) {
// if form has not been submitted
// display form
// if cookie already exists, pre-fill form field with cookie value
?>
<html>
<head></head>
<body>

<form action="<?php echo $_SERVER['PHP_SELF']?>" method="post">
Enter your email address: <input type="text" name="email" value="<?php echo $_COOKIE['email'] ?>" size="20">
<input type="submit" name="submit">
<?php
// also calculate the time since the last submission
if ($_COOKIE['lastsave']) {
$days = round((time() - $_COOKIE['lastsave']) / 86400)
echo " $days day(s) since last submission"
}
?>
</form>

</body>
</html>
<?php
}
else {
// if form has been submitted
// set cookies with form value and timestamp
// both cookies expire after 30 days
if (!empty($_POST['email'])) {
setcookie("email", $_POST['email'], mktime()+(86400*30), "/")
setcookie("lastsave", time(), mktime()+(86400*30), "/")
echo "Your email address has been recorded."
}
else {
echo "ERROR: Please enter your email address!"
}
}
?>
</body>
</html>