PHP-Code

<?php
  function reverse_add_blank(&$str){
    $len = strlen($str);
    for ($i=0; $i < $len; $i++) {
      $buffer = $str[$i];
      $str[$i] = $str[$len];
      $str[$len] = $buffer;
      $len--;
    }
    $str[strlen($str)] = " ";
  }

  $inputs = array();
  $inputs[] = "Hello World!";

  foreach ($inputs as &$value) {
    reverse_add_blank($value);
  }

  var_dump($inputs);

PHP-Code

<?php
$string = "Haha Hehe Hihi";
$array = str_split($string);

$ergebnis = reverse_add_blank($string, $array);
echo ($ergebnis);

function reverse_add_blank($string, $array)
{
	$erg = "";

	for($i = strlen($string)-1; $i >= 0; $i--)
	{
		$erg .= $array[$i];
		$erg .= " ";
	}

	return $erg;
}
?>

PHP-Code

<?php

$text = 'abc';

var_dump($text);

reverse_add_blank($text);

var_dump($text);

function reverse_add_blank(string &$value) : void
{
  $value = strrev($value); // reverse characters
  $value = implode(' ', str_split($value)); // convert string to array, then glue parts with whitespace together
}