Displaying username after they have logged in (newbie) - php

Question

Hello im completely new to php and my question is how can i echo out the username of the person who has logged in, on the page they get sent to after logging in successfully?
ive got the login system working and everything but not sure where to write the session stuff etc.
This is my login2a.php
$username = $_POST['username'];
$password = $_POST['password'];
$conn = mysqli_connect('localhost', 'root', '', 'assign02');
$username = mysqli_real_escape_string($conn, $username);
$query = "SELECT password, salt
FROM members
WHERE username = '$username';";
$result = mysqli_query($conn, $query);
if(mysqli_num_rows($result) == 0) // User not found. So, redirect to login_form again.
{
header('Location: login.html');
}
$userData = mysqli_fetch_array($result, MYSQL_ASSOC);
$hash = hash('sha256', $userData['salt'] . hash('sha256', $password) );
//check to see if the password is wrong if wrong redirect user to login forma again and if correct redirect to
if($hash == $userData['password'])
{
header('Location: signed_in.php?username = $username ');
//header('Location: login.html');
}else{ // Redirect to home page after successful login.
//header('Location: signed_in.php?username=$username');
header('Location: login.html');
}
?>
This is the page that i want their username to be displayed, this is just some parts of the website because its too big, what ive echoed is completely wrong i know but hope someone could help me with this problem. This page is the signed_in.php
<div class="layout-978">
<img id="content_background" src="Images/Background.png" />
<div class="main_content">
<div id="top_sellers_title">
<div class="col7">
<!--username displayed to show logged in-->
<?php
if (isset($_SESSION['username'])){
echo "<div id=\"welcome_msg\"> $username </div>";
}
?>

Answer 1

Modify this in your login page and don't forget to use session_start(); at the very beginning of your login page.
if($hash == $userData['password'])
{
$_SESSION['username'] = $username;
header('Location: signed_in.php');
//header('Location: login.html');
}
Then in signed_in.php page, to display the username just do the following
<?php
if(isset($_SESSION['username'])) echo '<div id="welcome_msg">'.$_SESSION['username']. '</div>';
?>

Answer 2

Use session_start() on top of both login2a.php and signed_in.php.
In your login2a.php file where you've successfully authenticated a user, create a session variable named username and assign the username you've passed to the query to that session variable. Here's how
.
.
.
if($hash == $userData['password'])
{
$_SESSION['username'] = $username;
// Continue with your code
}
Hope my answer helps