这个PHP脚本有什么问题

Hey all i am working on a simple registration form and i have done a simple test on it. basically i said if the username filed is empty and we click submit it will echo out 'all filed's are required' else Ok. My code looks fine or else i am going insane can some one have a look for me thank you :)

CODE:

<?php

  //require 'core.inc.php';



if(isset($_POST['username'])&& isset($_POST['password']) && isset($_POST['passwordAgain'])&& isset($_POST['Firstname'])&& isset($_POST['Lastname'])){

    $username = $_POST['username'];
    $password = $_POST['password'];
    $password_again = $_POST['passwordAgain'];
    $Firstname = $_POST['Firstname'];
    $Lastname = $_POST['Lastname'];

    if(!empty($username)){

        echo 'OK.';

    }else{

   echo 'fill in all details thank you';
     }


}

?>


<form action="join.inc.php" method="POST">


    Username: <input type="text" name="username" /><br />
    Password: <input type="password" type="password" /><br />
    Password Again: <input type="password" type="passwordAgain" /><br />
    FirstName: <input type="text" name ="Firstname"/><br />
    LastName: <input type="text" name ="Lastname" /><br />
    <input type="submit" value="SUBMIT" />
</form>

Rectify this:

 Password: <input type="password" name="password" /><br />
 Password Again: <input type="password" name="passwordAgain" /><br />

Your problem is in your HTML:

Password: <input type="password" type="password" /><br />
Password Again: <input type="password" type="passwordAgain" /><br />

You are specifying the type field twice instead of the name field.

what about giving a name for the submit button and try like this:

<input type="submit" name="sbmtBtn" value="SUBMIT" />

and submit part as:

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

$username = $_POST['username'];
$password = $_POST['password'];
$password_again = $_POST['passwordAgain'];
$Firstname = $_POST['Firstname'];
$Lastname = $_POST['Lastname'];

if($username && $password && $password_again && $Firstname && $Lastname))
{

    echo 'OK.';

}
else
{

    echo 'all fields are required.';
}


}