why session variable is empty to navigate the next page?

Question

I have been working is a website I have been dealing with a problem from a while, and now I know why it is happening, but not how to solve it. Please help!!

Page 1: In

Answer 1

use session in the start in first page, like this. Hopefully this will work

 <?php
session_start(); 
if (isset($_POST['sub'])) 
{
            $user=$_POST['user'];
            $pass=$_POST['pass'];
            $con=mysqli_connect("localhost","root","");
            $db=mysqli_select_db($con,"Database");
            $qry="select * from TABLE where username='$user' and password='$pass'";
            $res=mysqli_query($con,$qry)or die("could not connect to mysql");
            $row=mysqli_fetch_array($res);
            $len=mysqli_num_rows($res);
            if($len<=0)
             {
               echo"<script>";
               echo"alert('Oops.Username Or Password Incorrect!');window.location.href='login.php';";
               echo"</script>";
            }
           else
            {

        $_SESSION['id']=$row['id'];
        $_SESSION['message']=$user;
        $_SESSION['logout']="";
        $id=$_SESSION['id'];
        echo"<script>"; 
        echo"alert('log in Success $id ');window.location.href='login.php';"; //$id is print correctly 
        echo"</script>";
        }
    }

?>