gistfile1.php

<?php
$string = "1234567890";
$n = 3;
$numberOfCarachter = strlen($string);
$newStringArray = array();
$stringInitialPosition = 0;

echo "Number of Character: ".$numberOfCarachter."\n";

while($stringInitialPosition < $numberOfCarachter){
  echo "Initial Position: ".$stringInitialPosition."\n";
  echo "---------------------------------\n";
  
  $subString = substr($string, $stringInitialPosition, $n);

  echo "Substring: ".$subString."\n";
  
  $newStringArray[] = $subString;
  $stringInitialPosition += $n;
}
var_dump($newStringArray);

$newString = implode(' ', $newStringArray);

echo $newString."\n"; 

?>