Register.php

<?php
include 'core/init.php';
include 'includes/overall/header.php';
if (empty($_POST) === false) {
    $required_fields = array('username', 'password', 'password_again', 'first_name', 'last_name', 'email');
    foreach ($_POST as $key=>$value) {
        if (empty($value) && in_array($key, $required_fields) === true) {
            $errors[] = 'Fields marked with an asterisk are required';
            break 1;
        }
    }
    if (empty($errors) === true) {
        if (user_exists($_POST['username']) === true) {
            $errors[] = 'Sorry, the username \'' . $_POST['username'] . '\' is already in use.';
        }
        if (preg_match("/\\s/", $_POST['username']) == true) {
            $errors = 'Your username may not contain any spaces';
        }
        if (strlen($_POST['password']) < 8) {
            $errors[] = 'Sorry, Your password is not strong enough. Passwords are required to be atleast eight(8) characters long.';
        }
        if ($_POST['password'] !== $_POST['password_again']) {
            $errors[] = 'Your passwords do not match.';
        }
        if (filter_var($_POST['email'], FILTER_VALIDATE_EMAIL) === false) {
            $errors[] = 'A valid email address is required for registration';
        }
        if (email_exists($_POST['email']) === true) {
            $errors[] = 'Sorry, the email \'' . $_POST['email'] . '\' is already registered';
        }
    }
}
?>
<h2>Pilot Registration</h2>
<?php
if (isset($_GET['success']) && empty($_GET['success'])) {
    echo 'Registeration Successful!!!';
} else {
    if (empty($_POST) === false && empty($errors) === true) {
        $register_data = array(
            'username'      => $_POST['username'],
            'password'      => $_POST['password'],
            'first_name'    => $_POST['first_name'],
            'last_name'     => $_POST['last_name'],
            'email'         => $_POST['email']
        );
        register_user($register_data);
        header('Location: index.php');
        exit();

    } else if (empty($errors) === false) {
        echo output_errors($errors);
    }
    ?>
    <form action="" method="post">
        <ul>
            <li>
                Username*:<br>
                <input type="text" name="username" />
            </li>
            <li>
                Password*:<br>
                <input type="password" name="password" />
            </li>
            <li>
                Confirm Password*:<br>
                <input type="password" name="password_again" />
            </li>
            <li>
                First Name*:<br>
                <input type="text" name="first_name" />
            </li>
            <li>
                Last Name*:<br>
                <input type="text" name="last_name" />
            </li>
            <li>
                Email*:<br>
                <input type="text" name="email" />
            </li>
            <li>
                <input type="submit" value="Register" />
            </li>
        </ul>
    </form>
    <?php
    }
    include 'includes/overall/footer.php';?>