php username checker function

<?php
$username=array("admin","root","guest");



function  username_check($uname,$user_list) {


if(in_array($uname,$user_list)){

echo " username  is already selected";

exit();
}



else{
echo " access granted<br>";
}
}


username_check("root1",$username);


echo <<<WELCOME

<b> Welcome to my website</b>
WELCOME;

?>