<?php

if($_POST) {
    $username         = $_POST["username"];
    $password         = $_POST["password"];
    $confirm_password = $_POST["confirm_password"];

    if(empty($passowrd) || empty($confirm_password) || empty($username)) {
        exit("Blank fields.");
    }

    if($password != $confirm_password) {
        exit("Passwords do not match.");
    }

    $password = hash('whirlpool', $data);

    mysql_query("UPDATE `users` SET `password`='$password' WHERE `username`='$username'");

}
?>

<form name="testing" method="post" action="test.php">
    <label for="username">Username:</label> <input type="text" name="username" /><br />
    <label for="password">New Password:</label> <input type="text" name="password" /><br />
    <label for="confirm_password">Confirm New Password:</label> <input type="text" name="confirm_password" /><br /><br />

    <input type="submit" value="Submit" name="submit" />
</form>