setcookie / session register ? in my case

[nagasea]

Which one should I use setcookie / session register ?
Because Im facing this kind of problem :

index.php
<form action=\"admin.php\" method=\"post\">
<input type=\"hidden\" name=\"username\">
<input type=\"submit\" name=\"action\" value=\"ADD\">
</form>

admin.php
$username = $POST['username'];
if ($POST['action']=="ADD") {
echo $username;
}

book.php
what should I do If I still want to use Variable $username in this file (book.php) should I use setcookie/session register ? because I will use that $username in others page (book.php,author.php,title.php,etc)

thanks

[kevinsequeira]

on admin.php do this

admin.php

if ($POST['action']=="ADD") {
session_start();
session_register("username");
$username = $POST['username'];
}

book.php

session_start();
echo $HTTP_SESSION_VARS['username'];

reg
kevin