Question

I am playing with Twitter API. Some numbers (like Twitter ID) is really large such as 199693823725682700.

I’ve got this number as string format, and now I need to change it to just normal readable number, not like 1000xE09, because I need to substract -1 from that string-casted number. Then, I also need to send the number as string.

In sum, in PHP, how can I change the string a number, e.g., “199693823725682700” to another string “199693823725682699” (original number -1)?

Thanks a lot!

Answer 1

If BCMath is not available (it would be the preferable option if it is available) this function will decrement an arbitrarily sized integer stored as a string. There is no handling for floats or interpolation of scientific notation, it will only work with a string of decimal digits with an optional sign.

function decrement_string ($str) {

  // 1 and 0 are special cases with this method
  if ($str == 1 || $str == 0) return (string) ($str - 1);

  // Determine if number is negative
  $negative = $str[0] == '-';

  // Strip sign and leading zeros
  $str = ltrim($str, '0-+');

  // Loop characters backwards
  for ($i = strlen($str) - 1; $i >= 0; $i--) {

    if ($negative) { // Handle negative numbers

      if ($str[$i] < 9) {
        $str[$i] = $str[$i] + 1;
        break;
      } else {
        $str[$i] = 0;
      }

    } else { // Handle positive numbers

      if ($str[$i]) {
        $str[$i] = $str[$i] - 1;
        break;
      } else {
        $str[$i] = 9;
      }

    }

  }

  return ($negative ? '-' : '').ltrim($str, '0');

}

See it working