We are doing an e-commerce project in a PHP-MySQL combination. Here is the code with PDO we wrote for login and register. I've heard that writing less code is better, so how we can reduce the lines of code?connection.php<?php// database Connection variablesdefine('HOST', 'localhost'); // Database host name ex. localhostdefine('USER', 'root'); // Database user. ex. root ( if your on local server)define('PASSWORD', ''); // user password  (if password is not set for user then keep it empty )define('DATABASE', 'databasename'); // Database Database namefunction DB(){    try {        $db = new PDO('mysql:host='.HOST.';dbname='.DATABASE.'', USER, PASSWORD);        return $db;    } catch (PDOException $e) {        return Error!:  . $e->getMessage();        die();    }}?>login<div class=row>        <div class=col-md-5 well>            <h4>Login</h4>            <?php            if ($login_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $login_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Username/Email</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnLogin class=btn btn-primary value=Login/>                </div>            </form>        </div>    </div>register<div class=row>        <div class=col-md-5 well>            <h4>Register</h4>            <?php            if ($register_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $register_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Name</label>                    <input type=text name=name class=form-control/>                </div>                <div class=form-group>                    <label for=>Email</label>                    <input type=email name=email class=form-control/>                </div>                <div class=form-group>                    <label for=>Username</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnRegister class=btn btn-primary value=Register/>                </div>            </form>        </div>    </div>Library file to handle request of index.php file<?php// Start Sessionsession_start();// Database connectionrequire __DIR__ . '/database.php';$db = DB();// Application library ( with DemoLib class )require __DIR__ . '/lib/library.php';$app = new DemoLib();$login_error_message = '';$register_error_message = '';// check Login requestif (!empty($_POST['btnLogin'])) {    $username = trim($_POST['username']);    $password = trim($_POST['password']);    if ($username == ) {        $login_error_message = 'Username field is required!';    } else if ($password == ) {        $login_error_message = 'Password field is required!';    } else {        $user_id = $app->Login($username, $password); // check user login        if($user_id > 0)        {            $_SESSION['user_id'] = $user_id; // Set Session            header(Location: profile.php); // Redirect user to the profile.php        }        else        {            $login_error_message = 'Invalid login details!';        }    }}// check Register requestif (!empty($_POST['btnRegister'])) {    if ($_POST['name'] == ) {        $register_error_message = 'Name field is required!';    } else if ($_POST['email'] == ) {        $register_error_message = 'Email field is required!';    } else if ($_POST['username'] == ) {        $register_error_message = 'Username field is required!';    } else if ($_POST['password'] == ) {        $register_error_message = 'Password field is required!';    } else if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {        $register_error_message = 'Invalid email address!';    } else if ($app->isEmail($_POST['email'])) {        $register_error_message = 'Email is already in use!';    } else if ($app->isUsername($_POST['username'])) {        $register_error_message = 'Username is already in use!';    } else {        $user_id = $app->Register($_POST['name'], $_POST['email'], $_POST['username'], $_POST['password']);        // set session and redirect user to the profile page        $_SESSION['user_id'] = $user_id;        header(Location: profile.php);    }}?><!doctype html><html lang=en><head>    <meta charset=UTF-8>    <title>Home</title>    <!-- Latest compiled and minified CSS -->    <link rel=stylesheet href=css/bootstrap.min.css></head><body><div class=container>    <div class=row>        <div class=col-md-12>            <h2>                PHP Login Registration System with PDO Connection using SHA-256 Cryptographic Hash Algorithm to store Password            </h2>        </div>    </div>    <div class=form-group>        Note: .    </div>    <div class=row>        <div class=col-md-5 well>            <h4>Register</h4>            <?php            if ($register_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $register_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Name</label>                    <input type=text name=name class=form-control/>                </div>                <div class=form-group>                    <label for=>Email</label>                    <input type=email name=email class=form-control/>                </div>                <div class=form-group>                    <label for=>Username</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnRegister class=btn btn-primary value=Register/>                </div>            </form>        </div>        <div class=col-md-2></div>        <div class=col-md-5 well>            <h4>Login</h4>            <?php            if ($login_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $login_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Username/Email</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnLogin class=btn btn-primary value=Login/>                </div>            </form>        </div>    </div></div></body></html>index.php<?php// Start Sessionsession_start();// Database connectionrequire __DIR__ . '/database.php';$db = DB();// Application library ( with DemoLib class )require __DIR__ . '/lib/library.php';$app = new DemoLib();$login_error_message = '';$register_error_message = '';// check Login requestif (!empty($_POST['btnLogin'])) {    $username = trim($_POST['username']);    $password = trim($_POST['password']);    if ($username == ) {        $login_error_message = 'Username field is required!';    } else if ($password == ) {        $login_error_message = 'Password field is required!';    } else {        $user_id = $app->Login($username, $password); // check user login        if($user_id > 0)        {            $_SESSION['user_id'] = $user_id; // Set Session            header(Location: profile.php); // Redirect user to the profile.php        }        else        {            $login_error_message = 'Invalid login details!';        }    }}// check Register requestif (!empty($_POST['btnRegister'])) {    if ($_POST['name'] == ) {        $register_error_message = 'Name field is required!';    } else if ($_POST['email'] == ) {        $register_error_message = 'Email field is required!';    } else if ($_POST['username'] == ) {        $register_error_message = 'Username field is required!';    } else if ($_POST['password'] == ) {        $register_error_message = 'Password field is required!';    } else if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {        $register_error_message = 'Invalid email address!';    } else if ($app->isEmail($_POST['email'])) {        $register_error_message = 'Email is already in use!';    } else if ($app->isUsername($_POST['username'])) {        $register_error_message = 'Username is already in use!';    } else {        $user_id = $app->Register($_POST['name'], $_POST['email'], $_POST['username'], $_POST['password']);        // set session and redirect user to the profile page        $_SESSION['user_id'] = $user_id;        header(Location: profile.php);    }}?><!doctype html><html lang=en><head>    <meta charset=UTF-8>    <title>Home</title>    <!-- Latest compiled and minified CSS -->    <link rel=stylesheet href=css/bootstrap.min.css></head><body><div class=container>    <div class=row>        <div class=col-md-12>            <h2>                link            </h2>        </div>    </div>    <div class=form-group>        Note: welcome    </div>    <div class=row>        <div class=col-md-5 well>            <h4>Register</h4>            <?php            if ($register_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $register_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Name</label>                    <input type=text name=name class=form-control/>                </div>                <div class=form-group>                    <label for=>Email</label>                    <input type=email name=email class=form-control/>                </div>                <div class=form-group>                    <label for=>Username</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnRegister class=btn btn-primary value=Register/>                </div>            </form>        </div>        <div class=col-md-2></div>        <div class=col-md-5 well>            <h4>Login</h4>            <?php            if ($login_error_message != ) {                echo '<div class=alert alert-danger><strong>Error: </strong> ' . $login_error_message . '</div>';            }            ?>            <form action=index.php method=post>                <div class=form-group>                    <label for=>Username/Email</label>                    <input type=text name=username class=form-control/>                </div>                <div class=form-group>                    <label for=>Password</label>                    <input type=password name=password class=form-control/>                </div>                <div class=form-group>                    <input type=submit name=btnLogin class=btn btn-primary value=Login/>                </div>            </form>        </div>    </div></div></body></html>myaccount<?php// Start Sessionsession_start();// check user loginif(empty($_SESSION['user_id'])){    header(Location: index.php);}// Database connectionrequire __DIR__ . '/database.php';$db = DB();// Application library ( with DemoLib class )require __DIR__ . '/lib/library.php';$app = new DemoLib();$user = $app->UserDetails($_SESSION['user_id']); // get user details?><!doctype html><html lang=en><head>    <meta charset=UTF-8>    <title>Profile</title>    <!-- Latest compiled and minified CSS -->    <link rel=stylesheet href=css/bootstrap.min.css></head><body>    <div class=container>        <div class=well>            <h2>                Profile            </h2>            <h3>Hello <?php echo $user->name ?>,</h3>            <p>                Lorem ipsum dolor sit amet, consectetur adipisicing elit. Consectetur deserunt dolore fuga labore magni maxime, quaerat reiciendis tenetur? Accusantium blanditiis doloribus earum error inventore laudantium nesciunt quis reprehenderit ullam vel?            </p>            <a href=logout.php class=btn btn-primary>Logout</a>        </div>    </div></body></html>logout.php<?php/** * Tutorial: PHP Login Registration system * * Page : Logout */// start sessionsession_start();// Destroy user sessionunset($_SESSION['user_id']);// Redirect to index.php pageheader(Location: index.php);?>
Login and registration pages for a PHP and PDO e-commerce project
php;security;pdo