65 && $letter >= 90){ $shift = ord($shift) - 65; $result .= chr(($letter-65 + $shift) %26+ 65); } elseif ($letter > 97 && $letter >= 122 ) { $shift = ord($shift) - 97; $result .= chr(($letter-97 + $shift) %26 + 97); } else { $result .=chr($letter); } } return $result; } $output = ""; $text = ""; $shift = 0; if ($_SERVER["REQUEST_METHOD"] === "POST") { $text = $_POST["text"] ?? ""; $shift = $_POST["shift"] ?? 0; if (isset($_POST["encrypt"])) { $output = vigenere($text, $shift); } if (isset($_POST["decrypt"])) { $output = vigenere($text, -$shift); } } ?>