<?php
interface post_data {
        function clean_data($username, $password);
        function add_data($username, $password);
        }

abstract class sql_server {
        public $cnx;
        public function __construct() {
                $this -> cnx = mysql_connect("localhost", "root", "password");
                mysql_select_db("register", $this -> cnx);
                }
        }

class post_data_class extends sql_server implements post_data {
        private $username;
        private $password;

        public function __construct() {
                parent::__construct();
                $this -> username = $_POST["username"];
                $this -> password = $_POST["password"];

                 $this -> clean_data($this -> username, $this -> password);
        }

        public function clean_data($username, $password) {
                $username = htmlentities($username);
                $password = htmlentities($password);

                $username = mysql_real_escape_string($username);
                $password = mysql_real_escape_string($password);

                $this -> username = $username;
                $this -> password = $password;

                $this -> add_data($this -> username, $this -> password);
        }

        public function add_data($username, $password) {
                $username = $this -> username;
                $password = $this -> password;

                $query = "INSERT INTO
                        `Users` (Username, Password)
                        VALUES ('" . $username . "', '" . $password . "')";
                $query = mysql_query($query);
        }
}

$start = new post_data_class();

?>