Unable to display logged in user's id - php

Question

I imneed to display logged in/authenticated user's id in html page. My sign in script is below followed by the display script. I've been on it for quite a while. I need to display logged in user's id from the mysql database to html.
<?php
session_start();
include_once('server.php');
$error = false;
if(isset($_POST['btn-login'])){
$username = trim($_POST['username']);
$username = htmlspecialchars(strip_tags($username));
$password = trim($_POST['password']);
$password = htmlspecialchars(strip_tags($password));
if(empty($username)){
$error = true;
$errorUsername = 'Please Input Username';
}
if(empty($password)){
$error = true;
$errorPassword = 'Please Input Password';
}elseif(strlen($password)< 6){
$error = true;
$errorPassword = 'Password must be at least six characters';
}
if(!$error)
{
$password = md5($password);
$sql = "select * from users where username = '$username'";
$result = mysqli_query($conn, $sql);
$count = mysqli_num_rows($result);
$row = mysqli_fetch_assoc($result);
if($count==1 && $row['password'] == $password){
$_SESSION['username'] = $row['username'];
header('location: loggedin.php');
}else{
$errorMsg = 'Invalid Username or Password';
}
?>
//display script
<?php
session_start();
echo 'welcome user'.$_SESSION['id'];
?>

Answer 1

You need to set session like this.
$_SESSION['id'] = row['id'];
You are not getting the id value because $_SESSION['id'] is null.

Answer 2

to display the loged user
change this:
echo 'welcome user'.$_SESSION['id'];
to this:
echo 'welcome user'.$_SESSION['username'];
because $_SESSION['id'] is not set and you most probably dont want to show it in the html page so just use the user name or set it to somthing more natural like actual name if it exists in your db row.