login and logout the user

lesson 47.php
user visibke	we will run this page
<?php
require 'core.php';	template
require 'lesson44.php';	template
//include login , if we write outside the below if, it show s in or out of looged in, always shos logged in, for that purpose we will show
if (loggedin()){	in core page we used core
echo 'you are logged in!';	if written true, it will execute this loggedin
}else{
include 'login.php';
}
?>
}
?>
how to get the required row header related to username
how to logout the webpage after login
core.php
<?php
ob_start();
//to use header we have to start this
session_start();
$current_file = $_SERVER['SCRIPT_NAME'];
//IT WILL Bcarry basic data - it will give the url withoud domainname /login.php
function loggedin(){
if (isset($_SESSION['user_id']) && !empty($_SESSION['user_id'])){ return true;}
else{return false;}
}
function getuserfield($field){	write a function w
global $mycon;
$id = $_SESSION['user_id'];	get the id of that sesion and load into variable of that id
$query = "SELECT `$field` FROM `users` WHERE `id` = '$id' ";	run the query to , we gpt the one variable data, programm is asking row heading that’s want to get that and filters id of the required
if($query_run = mysqli_query($mycon, $query)){	run this query against database
$num_rows = mysqli_num_rows($query_run);	count the number of rows of that id with username
if($num_rows == 1)	if rows one ,
{$row = mysqli_fetch_row($query_run);	convert that row into array
return $row[0];	return that row with zero index
}
}
}
?>
logout.php
<?php
// session variable destroyed, session list empty, then core page , shows unset, it returns false, thne shows login page
require 'core.php';	to logout , stored session have to destroy
session_destroy();
header ('location: lesson47.php')	after destroy, it loads to this page , redirects
// after session destroyed go to this page means change in url with this name in ends
?>
user page
<?php
require 'core.php';
require 'lesson44.php';
//include login , if we write outside the below if, it show s in or out of looged in, always shos logged in, for that purpose we will show
$logout_text = '<br><a href="logout.php">logout </a>';	after log out,it have to logout page
if (loggedin()){
$firstname = getuserfield('firstname');	get the firstname of entered usernamae
$secondname = getuserfield('surname');	get the firstname of entered username
echo 'welcome, '.$firstname.' '. $secondname .' '.$logout_text ;	concatenate
}else{
include 'login.php';	if not , redirects to loginpage
}
?>

require require if else if failed to login , show the login page write a function to get the  function write a function to get relative firstname or last name of entered username function how to use outside variable inside pf function global how to get the session data $_session how to write a query to get the required row head data select from where how to execute query against database mysqli_query how to find how many number of rows mysqli_num_rows how to convert into array mysqli_fetch_row how to destroy the sessions session_destroy whweere to redirects after sessionis destroyed header