PHP writing a text file in the begin

So we are making in the class a sort of log. There is a input box and a button. Everytime the button is pressed, PHP will write on the text file and prints the current log. Now the text appears on the bottom, and we need to have the text appear on the top. Now how would we do that?

We tried doing this with alot of my classmates but it all resulted in weird behavours. (Like text is printed more then once, etc)

Thanks alot!

EDIT: Sorry, here is the code:

<html lang="en">
<head>
    <title>php script</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <form name="orderform" action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">  
    <input type="text" name="text"/>
    <input type="submit" value="Submit" />
    <?php
        //Basic variables
        echo("<br/>");
        $myFile = "log.txt";
        $logfile = fopen($myFile,'r+');
        $theData = fread($logfile,filesize($myFile));

        //Cookie stuff so the username is rememberd.
        $username = $_COOKIE['gebruikerscookie'];;
        if(isset($_POST['username'])){
            $gebruiker = $_POST['username'];
            if($_COOKIE['gebruikerscookie'] == $gebruiker){
                $username = $_COOKIE['gebruikerscookie'];
                echo("Welcome back");
            }else{
                setcookie("gebruikerscookie", $gebruiker);
                $username = $_COOKIE['gebruikerscookie'];
                echo("Welcome dude!");
            }           
        }

        //Checks if theres something inside 
        if(isset($_POST['text'])){
            $message = "<br/>". $username ." : " . $_POST['text'];
            fwrite($logfile, $message ,strlen($message));
        }
        echo($theData);
    ?>
    </form>
</body>

Solution

Check the fopen manual on modes: http://www.php.net/manual/en/function.fopen.php

Try 'r+' Open for reading and writing; place the file pointer at the beginning of the file.

Altough without any code this is hard to answer.