PHP Simple Chat room & debugging Issues

After entering the login.php program

<?php

Error_reporting (E_all^e_notice);

Session_Start (); Load session library, must be placed in the first row

$user _name=$_post["Nick"];

Session_register ("user_name"); Register the $user_name variable, note that there is no $ symbol

$_session[' user_name '];?>

<!--chat.php:My Chat room Main Page----------------------->

<title>my Chat Room </title>

<frameset rows= "80%,*" >

<frame src= "chat_display.php" name= "Chat_display" >

<frame src= "speak.php" name= "speak" >

</frameset>

appears during debugging: Undefined Index:user_name

Add error_reporting (E_all^e_notice) in front of the program to avoid mistakes.

PHP Simple Chat room & debugging Issues