I already build login system and I want to display username and first name when user logged in

See more:

SQL

PHP

MySQL

these code doesnt show any error but i am not getting username

function display_username() {
  //Start the Session


//3. If the form is submitted or not.
//3.1 If the form is submitted
if (isset($_POST['username']) and isset($_POST['password'])){
//3.1.1 Assigning posted values to variables.

//3.1.2 Checking the values are existing in the database or not
$query = "SELECT * FROM `users` WHERE username='$username' and password='$password'";
 
$result = mysqli_query($connection, $query) or die(mysqli_error($connection));
$count = mysqli_num_rows($result);
//3.1.2 If the posted values are equal to the database values, then session will be created for the user.
//if ($count == 1){
$_SESSION['username'] = $username;
//}else{
//3.1.3 If the login credentials doesn't match, he will be shown with an error message.
//$fmsg = "Invalid Login Credentials.";
//}
//}
//3.1.4 if the user is logged in Greets the user with message
if (isset($_SESSION['username'])){
$username = $_SESSION['username'];
echo "Hayyyyyy" . $username . "
";}

}

}

/****************Register user functions ********************/

function register_user($first_name, $last_name, $username, $email, $password) {


	$first_name = escape($first_name);
	$last_name  = escape($last_name);
	$username   = escape($username);
	$email      = escape($email);
	$password   = escape($password);



	if(email_exists($email)) {


		return false;


	} else if (username_exists($username)) {

		return false;

	} else {

		$password   = md5($password);

		$validation_code = md5($username . microtime());

		$sql = "INSERT INTO users(first_name, last_name, username, email, password, validation_code, active)";
		$sql.= " VALUES('$first_name','$last_name','$username','$email','$password','$validation_code', 0)";
		$result = query($sql);
		confirm($result);


		$subject = "Activate Account";
		$msg = " Please click the link below to activate your Account
		http://omilearn.com/activate.php?email=$email&code=$validation_code
		";

		$headers = "From: noreply@omilearn.com";



		send_email($email, $subject, $msg, $headers);


		return true;

	}



}

<pre lang="PHP">

/****************Validation functions ********************/



function validate_user_registration(){

$errors = [];

$min = 3;
$max = 20;



// if($_SERVER['REQUEST_METHOD'] == "POST") {
if (isset($_POST['register-submit'])) {

$first_name = clean($_POST['first_name']);
$last_name = clean($_POST['last_name']);
$username = clean($_POST['username']);
$email = clean($_POST['email']);
$password = clean($_POST['password']);
$confirm_password = clean($_POST['confirm_password']);



if(strlen($first_name) < $min) {

$errors[] = "Your first name cannot be less than {$min} characters";

}

if(strlen($first_name) > $max) {

$errors[] = "Your first name cannot be more than {$max} characters";

}




if(strlen($last_name) < $min) {

$errors[] = "Your Last name cannot be less than {$min} characters";

}


if(strlen($last_name) > $max) {

$errors[] = "Your Last name cannot be more than {$max} characters";

}

if(strlen($username) < $min) {

$errors[] = "Your Username cannot be less than {$min} characters";

}

if(strlen($username) > $max) {

$errors[] = "Your Username cannot be more than {$max} characters";

}


if(username_exists($username)){

$errors[] = "Sorry that username is already is taken";

}



if(email_exists($email)){

$errors[] = "Sorry that email already is registered";

}




if(strlen($email) < $min) {

$errors[] = "Your email cannot be more than {$max} characters";

}

if($password !== $confirm_password) {

$errors[] = "Your password fields do not match";

}



if(!empty($errors)) {

foreach ($errors as $error) {

echo validation_errors($error);


}


} else {


if(register_user($first_name, $last_name, $username, $email, $password)) {



set_message("

Please check your email or spam folder for activation link

");

redirect("index.php");


} else {


set_message("

Sorry we could not register the user

");

redirect("index.php");

}



}



} // post request



} // function

What I have tried:

i tried many codes but didnt work
<?php display_username('$username'); ?>
<?php $_SESSION['username'] ?>
<?php
session_start();
echo $_SESSION['username']; ?>;

function display_username() {

$query=mysqli_query($con, ‘SELECT username FROM users WHERE users=”$_SESSION[‘username’]”’);

$fetch=mysqli_fetch_assoc($con, $query);

$userNameToShow = $fetch[‘username’];


}

<?php display_username() ?>


if(isset($_SESSION['email'])