on page refresh POST array do not get empty - php

Question

I created a form in php with action as the same page url and method as POST
<?php
if(isset($_POST['submitted']) && $_POST['submitted'] != ''){
echo $_POST['fname'];
echo "<br />";
echo $_POST['lname'];
echo "<br />";
echo $_POST['submitted'];
}
?>
<h1>testing...</h1>
<form action="test.php" method="POST">
First Name: <input type="text" name="fname" />
Last Name: <input type="text" name="lname" />
<input type="submit" name="submitted" />
</form>
When I enter data and submit it, page shows the data as I printed the data. But when I refresh page the data still exists, I want the data to be shown only when I click submit.
Can anybody help me in this?
Am I doing something wrong.

Answer 1

AFAIK. This is a standard browser behavior to repeat last request with f5 button.
My understanding for what do you need to prevent it. It's to prevent 'spam'.
So, you need to understand that first submit was already made.
As test idea you can add timestamp for send button and check it on send. In this case timestamp from button and on send will be different for refreshing

Answer 2

I figured out that
0) {
$_SESSION['shout'] = $_POST['shout'];
header("HTTP/1.1 303 See Other");
header("Location: http://$_SERVER[HTTP_HOST]/echochamber.php");
die();
}
else if (isset($_SESSION['shout'])){
$echoedShout = $_SESSION['shout'];
/*
Put database-affecting code here.
*/
session_unset();
session_destroy();
}
?>
OR I did that in codeigniter using set_flashdata which stores session data for next request only.