Number to words in PHP

Source code viewer
  /**
   * Helper function for converting numbers to words.
   *
   * @param int $num
   *   Integer that is going to be converted to words.
   *
   * @return string
   *   Return the number in words.
   */
function NumberToWord($num) {
  $words = array();
  $list1 = array(
    '', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine',
    'ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen',
    'seventeen', 'eighteen', 'nineteen',
  );
  $list2 = array(
    '', 'ten', 'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy',
    'eighty', 'ninety', 'hundred',
  );
  $list3 = array(
    '', 'thousand', 'million', 'billion', 'trillion', 'quadrillion',
    'quintillion', 'sextillion', 'septillion', 'octillion', 'nonillion',
    'decillion', 'undecillion', 'duodecillion', 'tredecillion',
    'quattuordecillion', 'quindecillion', 'sexdecillion', 'septendecillion',
    'octodecillion', 'novemdecillion', 'vigintillion',
  );
  $num_length = strlen($num);
  $levels = (int) (($num_length + 2) / 3);
  $max_length = $levels * 3;
  $num = substr('00' . $num, - $max_length);
  $num_levels = str_split($num, 3);
  for ($i = 0; $i < count($num_levels); ++$i) {
    $levels--;
    $hundreds = (int) ($num_levels[$i] / 100);
    $hundreds = ($hundreds ? ' ' . $list1[$hundreds] . ' hundred' . ' ' : '');
    $tens = (int) ($num_levels[$i] % 100);
    $singles = '';
    if ($tens < 20) {
      $tens = ($tens ? ' ' . $list1[$tens] . ' ' : '');
    }
    else {
      $tens = (int) ($tens / 10);
      $tens = ' ' . $list2[$tens] . ' ';
      $singles = (int) ($num_levels[$i] % 10);
      $singles = ' ' . $list1[$singles] . ' ';
    }
    $words[] = $hundreds . $tens . $singles . (($levels && (int) $num_levels[$i]) ? ' ' . $list3[$levels] . ' ' : '');
  }
 
  return implode(' ', $words);
}
Programming Language: PHP