POST Validation Loop

Assumptions

You have an HTML form with a variety of inputs. The action attribute of the form points to a PHP file that contains the code below.

Notes about code

This code starts by creating an array that holds the name of various inputs being submitted via a POST. getFormData() is then called, where the required fields are passed in. Inside the function an array is created to hold various pieces of data related to the form. $formData['valid'] is a boolean referencing if all data was provided and valid, $formData['fields'] is an array keyed by the name of the input with their respective value from the POST data, $formData['notValidFields'] is an array that will contain the names of any inputs that were not passed or that had non-valid data.
This logic can be easily extended with regular expressions to check for stricter data, such as email addresses and urls.

<?php

$requiredFields = array('field1', 'field2', 'field3', 'field4');
$formData = getFormData($requiredFields);

function getFormData($requiredFields){
       $formData = array();
       $formData['valid'] = true;
       $formData['fields'] = array();
       $formData['notValidFields'] = array();

       for($a = 0; $a < count($requiredFields); $a++){
               $field = $requiredFields[$a];
               if(isset($_POST[$field])){
                       $value = $_POST[$field];
                       if(empty($value)){
                               $formData['valid'] = false;
                               $formData['notValidFields'][] = $field;
                       }else{
                               $formData['fields'][$field] = $value;
                       }
               }else{
                       $formData['valid'] = false;
                       $formData['notValidFields'][] = $field;
               }
       }
       return $formData;
}