I'm trying to write some PHP code to perform a simple form validation. I've been using Kevin Yank's book which suggests redirecting to a separate error page if the data does not match a field's criteria. However, I would like error messages to appear for specified fields directly on the form where required (whilst retaining all data client has already entered) and only proceed to validation once all criteria are satisfied.

It is just the 'prod_name' and 'theatre_name' fields that the client needs to enter, and at the moment I just want it to prevent empty fields being entered.

I've been trying to find an easy-to-follow tutorial, but they all seem a bit advanced for what I am capable of (still a beginner...).

Below are excerpts from my main php index, and the html.php form (let me know if you need any more):-

Any advice or directions to a good tutorial much appreciated!



PHP Code:
include_once $_SERVER['DOCUMENT_ROOT'] . '/includes/magicquotes.inc.php';

if (isset(
$_GET['add'])) //CODE ACTIVATED IF 'Add new production' LINK IS USED
$pagetitle 'New Production';
$pagedescription 'Add a new production to the database';
$action 'addform';
$prod_id '';
$prod_name '';
$prod_created 'TBC';
$prod_updated 'TBC';
$theatre_id '';
$theatre_name '';
$button 'Submit';
$error '';


if (isset(
$_SERVER['DOCUMENT_ROOT'] . '/includes/db.inc.php';

$prod_name mysqli_real_escape_string($link$_POST['prod_name']);
$theatre_name mysqli_real_escape_string($link$_POST['theatre_name']);

    if (
$prod_name == '' || $theatre_name == '')
$pagetitle 'Error';
$error 'You must enter all the fields.';
It then goes on to use SQL commands to enter data into the database.

PHP Code:
<form action="?<?php htmlout($action); ?>" method="post">
            <div class="labelcontainer">
                <div id="box2">    

                    <label for="prod_name" class="fixedwidth">Production Name: <input type="text" name="prod_name" id="prod_name" value="<?php htmlout($prod_name); ?>" class="entryfield"/></label>
                    <h4>i.e. Hamlet</h4>
                    <label for="theatre_name" class="fixedwidth">Theatre: <input type="text" name="theatre_name" id="theatre_name" value="<?php htmlout($theatre_name); ?>" class="entryfield"/></label>
                    <h4>i.e. Donmar Warehouse (Covent Garden, London)</h4>
                </div> <!-- end of box div --!>        
            </div> <!-- end of labelcontainer div --!>
            <input type="hidden" name="prod_id" value="<?php htmlout($prod_id); ?>"/>
            <input type="hidden" name="theatre_id" value="<?php htmlout($theatre_id); ?>"/>
            <input type="submit" value="<?php htmlout($button); ?>" class="button"/>