Challenge 3 — Solution

Task: Given a simulated $_POST array representing a contact form (name,
email, message — but with "email" deliberately missing), loop over
$_POST with foreach and print_r any keys that are empty or missing,
using isset() to check each expected field safely.

<?php
    // Simulating a submitted contact form with "email" missing
    $_POST = [
        "name" => "Alex",
        "message" => "Hello, I have a question."
    ];

    $expectedFields = ["name", "email", "message"];
    $missing = [];

    foreach ($expectedFields as $field) {
        if (!isset($_POST[$field]) || $_POST[$field] === '') {
            $missing[] = $field;
        }
    }

    print_r($missing);
?>


Output:
Array
(
    [0] => email
)

Notes:
- $expectedFields lists every field the form is supposed to contain,
  independent of whatever actually arrived in $_POST.
- isset($_POST[$field]) safely checks for each expected key without
  triggering an "undefined array key" warning, exactly per the
  chapter's own safe-access guidance.
- The || $_POST[$field] === '' check also catches a field that exists
  but was submitted completely empty - isset() alone only detects a
  genuinely missing key, not a present-but-blank one.
- Only "email" ends up in $missing, since "name" and "message" were
  both present and non-empty in the simulated $_POST array.