How do I write a script that finds the first character and its position that is different between 2 strings same length?

<?php

  // provide your strings.
  $word1 = "Insert first string here";
  $word2 = "Insert second string here";

  // figure out how many characters your strings have.
  $totalCharacters = strlen($word1);

  // convert each string to an array of its characters
  $array1 = str_split($word1);
  $array2 = str_split($word2);

  // loop through the array elements one at a time.
  // each time, check to see if the first array element is the same as the second array element.
  // if they're the same, it goes back around.
  // if they're different, the character in both arrays and the character number ...
  // are all set as variables, and the for loop is broken.

  for ($i = 0; $i <= $totalCharacters; $i++) {

    if ( $array1[$i] !== $array2[$i] ) {

      $firstCharacter1 = $array1[$i];
      $firstCharacter2 = $array2[$i];
      $itsPosition = $i + 1; // adding 1 since the array's character count starts at zero (1 is easier for humans)
      break;

    } // end IF condition

  } // end FOR loop

  // echo out your results

  if ( !isset($itsPosition) ) {
    echo "Strings are identical.";
  } else {
    echo "The first difference occurs at character # " . $itsPosition . " of the strings. 
    It is " . $firstCharacter1 . " in the first string,
    and " . $firstCharacter2 . " in the second string.";
  }

?>