PHP Web Form Error Display - php

Question

I am a PHP newb. I have the following code for a web form. It works fine as is, but I would like to do the following:
Return the errors as an array (?) so I can display errors as individual lines under each input.
and
Disallow the form from being able to be submitted twice.
Any help would be greatly appreciated.
<form id="form1" method="post" action="<?= $_SERVER['PHP_SELF'] ?>">
<fieldset>
<legend>Contact Me</legend>
<?php
if (isset($_POST['Submit'])) {
if ($_POST['firstname'] != "") {
$_POST['firstname'] = filter_var($_POST['firstname'], FILTER_SANITIZE_STRING);
if ($_POST['firstname'] == "") {
$errors .= 'Please enter a valid first name.<br/><br/>';
}
} else {
$errors .= 'Please enter your first name.<br/>';
}
if ($_POST['lastname'] != "") {
$_POST['lastname'] = filter_var($_POST['lastname'], FILTER_SANITIZE_STRING);
if ($_POST['lastname'] == "") {
$errors .= 'Please enter a valid last name.<br/><br/>';
}
} else {
$errors .= 'Please enter your last name.<br/>';
}
if ($_POST['email'] != "") {
$email = filter_var($_POST['email'], FILTER_SANITIZE_EMAIL);
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
$errors .= "$email is <strong>NOT</strong> a valid email address.<br/><br/>";
}
} else {
$errors .= 'Please enter your email address.<br/>';
}
if ($_POST['message'] != "") {
$_POST['message'] = filter_var($_POST['message'], FILTER_SANITIZE_STRING);
if ($_POST['message'] == "") {
$errors .= 'Please enter a message to send.<br/>';
}
} else {
$errors .= 'Please enter a message to send.<br/>';
}
if (!$errors) {
$mail_to = '***#****.com';
$subject = 'New Mail from Web Site';
$message = 'From: ' . $_POST['firstname'] . " " . $_POST['lastname'] . "\n";
$message .= 'Email: ' . $_POST['email'] . "\n";
$message .= "Message:\n" . $_POST['message'] . "\n\n";
mail($mail_to, $subject, $message);
echo "<p>Thank you for your email!<br/><br/></p>";
} else {
echo '<div style="color: #00CC00">' . $errors . '<br/></div>';
}
}
?>
<label>First Name:</label>
<input type="text" name="firstname" value="<?php echo $_POST['firstname']; ?>" size="50" />
<label>Last Name:</label>
<input type="text" name="lastname" value="<?php echo $_POST['lastname']; ?>" size="50" />
<label>Email Address:</label>
<input type="text" name="email" value="<?php echo $_POST['email']; ?>" size="50"/>
<label>Message:</label>
<textarea name="message" rows="5" cols="50"><?php echo $_POST['message']; ?></textarea>
<br/>
<input type="submit" class="moveright" name="Submit" value="Submit" />
</fieldset>
</form>

Answer 1

You can use an array for the errors instead of concatenating them into one string. Then you can check for each error at the specified form input.
Sample error check
// instead of: $errors .= 'Please enter a message to send.<br/>';
if ($_POST['message'] == "")
$errors['message'] = 'Please enter a message to send.<br/>';
Sample error display
<label>Message:</label>
<?php if ($errors['message'] != "") echo $errors['message']; ?>
<textarea name="message" rows="5" cols="50"><?php echo $_POST['message']; ?></textarea>

Answer 2

Instead of appending each error to the string, do like the following:
$errors[] = 'error text';
EDIT: as the others have said, it's good practice to initialize the array before starting to set the values, like so: $errors = array();
As for the disallowing the form to be submitted twice, that needs javascript. Here's a link to help: http://www.webmasterworld.com/forum91/3781.htm

Answer 3

To make your errors into an array, initialize it before form processing as:
$errors = array();
if (isset($_POST['Submit'])) {
...
Each time you have an error, rather than concatenating it on with .=, use the [] array append syntax:
$errors[] = 'Please enter a message to send.';
To prevent the form from being submitted twice, we often use a variable in $_SESSION to indicate that it has been completed. On successful submission, set a $_SESSION['success'] flag. Don't forget also to initialize the session at the start of the script:
session_start();
$_SESSION['success'] = FALSE;
$errors = array();
// Only process the form if the session flag isn't set:
if (isset($_POST['Submit']) && !$_SESSION['success']) {
...
// Later, on success,
echo "<p>Thank you for your email!<br/><br/></p>";
// Set the flag to prevent resubmission.
$_SESSION['success'] = TRUE;