Notes

<?php
//Start a session.
session_start();

//Adds a header and a footer.
include 'header.php';

if (isset($_SESSION['tempUserId'])){
header('Location:index.php');
}

//Connects to database.
$connect = new PDO('mysql:dbname=electronics;host:localhost','root','');

//If login is submitted.
if(isset($_POST['login'])){
$connectVariable = $connect->prepare("SELECT * FROM tbl_customers WHERE username = :username");
$criteria=[
'username'=>$_POST['username']
];
$connectVariable->execute($criteria);//Executes the criteria.

if($connectVariable->rowCount()>0){
$user = $connectVariable->fetch();// This return a row from the result as array.

if (password_verify($_POST['password'], $user['password'])) { //Checks the entered password with the password saved in the database.
$_SESSION['tempUserId'] = $user['user_id'];
$_SESSION['tempUserId'] = 1;
header('Location:index.php'); //redirects to the home page.
}
else
echo "Password was incorrect";//Displays if password is incorrect.
}
else
echo "Login failed. Try again";//Displays if invalid or empty data is entered
}
?>
<!--Login form-->
<h4>Login Here</h4>

<form action="login.php" method="POST">
<label> Username : </label><br><br>
<input type="text" name="username"></input><br><br>

<label> Password : </label><br><br>
<input type="password" name="password"></input><br><br>

<input type="submit" name="login" value="login" ></input><br><br>

<a href="register.php">Register Here</a><br><br><!--Link to register page-->
</form>