How to account for spaces and numbers in Caesar's cipher?

Question

I am trying to encrypt a message using CAESAR'S CIPHER and the encryption also works correctly. But now I would like to know how to account for spaces and numbers in the string to be encrypted.

PHP

<?php
//the text to be encrypted
$plain_text='ABC';
 echo $plain_text."<br>";
//letters of alphabet array
$alphabet=array('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 
'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z');
//positions of the letters in alphabet
$flip=array_flip($alphabet);

//plaintext array
$plain_text=str_split($plain_text);
$n=count($plain_text);
$encrypted_text='';
for ($i=0; $i<$n; $i++){
    //encryption
    $encrypted_text.=$alphabet[($flip[$plain_text[$i]]+2)%26];
}

echo $encrypted_text;
?>

Answer 1

Like this

<?php
    //the text to be encrypted
    $plain_text='ABC';
     echo $plain_text."<br>";
    //letters of alphabet array
    $alphabet=array('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 
    'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '1','2','3','4','5','6','7','8','9','0',' ');
    //positions of the letters in alphabet
    $flip=array_flip($alphabet);
    $mod = count( $alphabet );

    //plaintext array
    $plain_text=str_split($plain_text);
    $n=count($plain_text);
    $encrypted_text='';
    for ($i=0; $i<$n; $i++){
        $n = strtoupper( $n );
        //encryption
        $encrypted_text.=$alphabet[($flip[$plain_text[$i]]+2) % $mod];
    }

    echo $encrypted_text;
?>

Add them to your list and make the $mod dynamic based on the count, I'd add strtoupper to account for lowercase letters.

That said, this isn't your homework is it? You can put anything you like in there as long as its not a duplicate, if you want to error check for duplicates then just

   $alphabet = array_unique($alphabet);

To be sure you never put a duplicate in the array, but that might be overkill.