PHP program to convert string to lowercase without using the library function

<?php
//function definition
//this function accepts a string/text, converts
//text to lowercase and return the lowercase converted string
function lowercase($str)
{
    $chars  = str_split($str);
    $result = '';

    //loop from 0th character to the last character
    for ($i = 0; $i < count($chars); $i++) {
        //extracting the character and getting its ASCII value
        $ch = ord($chars[$i]);

        //if character is a lowercase alphabet then converting 
        //it into an lowercase alphabet
        if ($chars[$i] >= 'A' && $chars[$i] <= 'Z')
            $result .= chr($ch + 32);
        else
        $result .= $chars[$i];
    }
    //finally, returning the string
    return $result;
}

//function calling
$text = "HELLO WORLD";
echo lowercase($text);
echo "<br>";

$text = "Hello world!";
echo lowercase($text);
echo "<br>";

$text = "Hello@123.com";
echo lowercase($text);
echo "<br>";

?>

Output

hello world
hello world!
hello@123.com