Caesar cipher

caesar-cipher.php

<?php
/**
 * @author Subin Siby <subinsb.com>
 */
function getInput()
{
    return trim(fgets(STDIN));
}

function encrypt($i, $k)
{
    $s = str_split('abcdefghijklmnopqrstuvwxyz');
    $n = '';

    foreach (str_split($i) as $l) {
        if (!ctype_alpha($l)) {
            $n .= $l;
            continue;
        }

        $charPos = array_search(strtolower($l), $s) + $k;
        $encChar = $s[($charPos > 25 ? $charPos - 26 : $charPos)];

        if (ctype_upper($l)) {
            $n .= strtoupper($encChar);
        } else {
            $n .= $encChar;
        }

    }
    return $n;
}

echo 'Enter string to encrypt:' . PHP_EOL;
$i = getInput();
echo 'Enter key:' . PHP_EOL;
$k = getInput();
echo 'Your encrypted string:' . PHP_EOL . encrypt($i, $k) . PHP_EOL;

Try it out : https://eval.in/857751