ipad php session issue / not working

I have user login script, user session destroyed when redirect the page.

Here is the code:

session_start() ;

if ( $_SESSION["logged_in"] != 1 )
{
    header("Location: index.php");
}

Need to add exit to fix session destroyed issue. 
session_start() ;

if ( $_SESSION["logged_in"] != 1 )
{
    header("Location: index.php");
 
    exit;
}