<?php
if (!$_POST['submit'])
{
form();
} else {
if (empty($_POST['first_name'])) { $error0='<br>First Name'; }

if (empty($_POST['surname'])) { $error1='<br>Surname'; }

if(!eregi("^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,3})$", $_POST['email_address'])) { $error2='<br>Valid e-mail address'; }

$error_messages = $error0.$error1.$error2;
if ($error_messages)
{
echo "Please ensure the following fields are completed before submitting your form:<strong>". $error_messages ."</strong><br><br>";

form();

} else {

echo "Thank you for completing the form. Please <a href="form.php">click here</a> to contine....";
}}
?>

<?php
function form()
{
echo "<form method="post" action="">";

echo "First Name: <input type="text" name="first_name" size="35" value="". $_POST['first_name'] . ""><br>";

echo "Surname: <input type="text" name="surname" size="35" value="". $_POST['surname'] . ""><br>";

echo "Email Address: <input type="text" name="email_address" size="35" value="". $_POST['email_address'] . ""><br>";

echo "<input type="submit" name="submit" value="Submit Form">";

echo "</form>";
}

?>