Kod1

<?php

if (isset($_POST['submitButton'])) {

    require 'dbh.inc.php';

    $username = $_POST['username'];
    $password = $_POST['password'];
    $rePassword = $_POST['rePassword'];

    if (empty($username) || empty($password) || empty($rePassword)) {
        header('Location: signup.php?error=empty_inputs');
        die();
    }

    if (strlen($username) < 5) {
        header('Location: signup.php?error=2shortusername');
        die();
    }

    if (strlen($password) < 8) {
        header('Location: signup.php?error=2shortpassword');
        die();
    }

    if ($password !== $rePassword) {
        header('Location: signup.php?error=pwddontmatch');
        die();
    }
}

if (isset($_GET['error'])) {

    switch($_GET['error']) {

        case 'empty_inputs':
        echo 'Please fill in all fields.';
        break;

        case '2shortusername':
        echo 'Your username must be atleast 5 characters long.';
        break;

        case '2shortpassword':
        echo 'Your password must be atleast 8 characters long.';
        break;

        case 'pwddontmatch':
        echo 'Your passwords do not match';
        break;

        default:
        echo 'Unknown error.';
        break;

    }

}