javascript - PHP UPDATE with if and else statement -

i need little script, making library sign in/out , page , have working posts form when sign in , out, want make if trying sign out , never signed in pop-up js alert tell them , can't quite it.

here's code:

<?php     session_start();     include_once("connect.php");     date_default_timezone_set("america/winnipeg");     $date = ("m-d-y");     $timeout = date("g:i:s a");      //search existing entries     if ("select exists(select * signin_out     lname='".$_post['lastname']."' , fname='".$_post['firstname']."'      , date='".$date."')") {          //if exist run         mysql_query("update signin_out set timeout='" . $timeout . "'              lname='" . $_post['lastname'] . "'              , fname='" . $_post['firstname'] . "' , timeout='' ");         header("location: ../index.html");          //if don't exist run     } else {         header("location: ../index.html");         echo "<script type='text/javascipt'>\n";         echo "alert('you did not sign in!');\n";         echo "</script>";    } ?> 

the http location header sends them ../index.html long before javascript gets echoed out. need have logout.php page javascript or $_get variable page redirect them to, , trigger alert box there.

for instance:

... } else {     header('location: ../index.php?notloggedin'); } 

and somewhere in index.php:

<?php if(isset($_get['notloggedin'])) {     echo '<script>alert("you did not sign in!");</script>'; } ?> 

although find alert box rather intrusive, i'd rather do:

<?php if(isset($_get['notloggedin'])) {     echo '<p><strong>you did not sign in!</strong></p>'; } ?>