function reverseWord(&$str, $word) {
$pos = strpos($str, $word);
if ($pos !== false) {
$reversed = strrev($word);
$str = substr($str, 0, $pos) . $reversed . substr($str, $pos + strlen($word));
}
}
$str = "C++ C Java Python PHP C#";
$word = "Java";
reverseWord($str, $word);
echo $str . PHP_EOL;
/*
run:
C++ C avaJ Python PHP C#
*/