User Registration

Key Techniques Used

Self-posting form: action="" posts to same script
Field preservation: value="<?= htmlspecialchars($field) ?>"
Per-field errors: Check $errors['field'] existence
Checkbox handling: isset($_POST['name']) (only sent if checked)

The Validation Pattern

<?php
$errors = [];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = trim($_POST['username'] ?? '');

    // Validation rules
    if (empty($username)) {
        $errors['username'] = 'Username is required';
    } elseif (strlen($username) < 3) {
        $errors['username'] = 'Username must be at least 3 characters';
    }

    // Process only if no errors
    if (empty($errors)) {
        // Save to database, send email, etc.
        header('Location: success.php');
        exit;
    }
}
?>

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