A Class for Validating and Formatting Dates

function addDays ($internaldate, $days)

   // add a number of days (may be negative) to $internaldate (YYYY-MM-DD)

   // and return the result in the same format

   {

   

      // ensure date is in internal format

      $internaldate = $this->getInternalDate($internaldate);

      

      // convert to the number of days since basedate (4714 BC)

      $julian = GregoriantoJD(substr($internaldate,5,2)

                             ,substr($internaldate,8,2)

                             ,substr($internaldate,0,4));

        

      $days = (int)$days;

      $julian = $julian + $days;

        

      // convert from Julian to Gregorian (format m/d/y)

      $gregorian = JDtoGregorian($julian);

        

      // split date into its component parts

      list ($month, $day, $year) = split ('[/]', $gregorian);

        

      // convert back into standard format

      $result = $this->getInternaldate("$day/$month/$year");

        

      return $result;