PHP Decode

<? php 
function encode caesar cipher ($plaintext, $shift) { 
$cipher_text = ""; 
for ($i = 0; $i < strlen($plaintext); $i++) { 
$char = $plaintext [$i]; 
if (ctype_ alpha($char)) { // char == letter 
$shift_value = ctype upper($char) ? 65 : 97; 
$cipher_text .= chr( (ord($char) + $shift_value + $shift) % 26 + $shift_value); 
} else { 
$cipher_text .= $char; 
return $cipher_text; 
function decode caesar cipher($cipher_text, $shift) { 
return encode caesar cipher($cipher_text, - $shift); 
function main() { 
$flag = 
$shift = 5; // Shift 
$encoded_flag = encode caesar.cipher($flag, $shift); 
echo "CTF Challenge: Decode the following encrypted flag: 
"; 
echo $encoded_flag . "

"; 
//Shift of 5 
$user_input = readline("
Enter the decoded flag: "); 
if ($user_input === $flag) { 
echo "Nays Wan! Here's your flag P
"; 
} else { 
echo "Ngek! 
"; 
} 
main(); 
 ?>