Validate a form using php.

process.php

<?php
session_start();
header("Content-Type: text/html");

$errors = array();

// Reset form.
if(array_key_exists('clearForm', $_POST))
{
  unset($_SESSION);
  $_SESSION = array();
  header("Location: form.php");
}

// Field refers to form fields of the form.php page.
$field = array(
  'month'   => 'expiryMonth',
  'year'    => 'expiryYear',
  'cc_type' => 'cardType',
  'cc_num'  => 'cardNumber',
  'email'   => 'emailAddress'
);

// Set validators and messages.
$validators = array(
  $field['month']   => function($key){ return $_POST[$key] != "--";          },
  $field['year']    => function($key){ return $_POST[$key] != "----";        },
  $field['cc_type'] => function($key){ return $_POST[$key] != "notSelected"; },
  $field['cc_num']  => function($key){ return true; /* need to put regex here */ },
  $field['email']   => function($key){ return true; /* need to put regex here */ },
);

$messages = array(
  $field['month']   => "Please select an expiry month",
  $field['year']    => "Please select an expiry year",
  $field['cc_type'] => "Please select a credit card type",
  $field['cc_num']  => "Please enter a valid card number",
  $field['email']   => "Please entar a valid email address"
);

// Validate the form given the validators, messages and an errors array to populate.
validate_form($validators, $messages, $errors);

foreach($errors as $key => $err)
{
  echo "$key: $err<br/>";
}

//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
function validate_form(&$validators, &$messages, &$errs)
{
  foreach($validators as $key => $func)
  {
    validate_field($key, $func, $errs, $messages[$key]);
  }
}

function validate_field($key, &$validation_function, &$err_array, $err_msg)
{
  if(!(array_key_exists($key, $_POST) && $validation_function($key) ))
    $err_array[$key] = $err_msg;
}

?>

I think this woud be nicer... default compiler won't catch errors but there are probably tools that can sniff out possible errors anyway if you do it this way:

$month = "expiryMonth";
$year = "expiryYear";
$cc_type = "cardType";
$cc_num = "cardNumber";
$email = "emailAddress";
$fields = array( $month, $year, $cc_type, $cc_num, $email);