Calculate an average date in C++ based on array of dates

gistfile1.txt

int wean_dates_size = bgi->wean_dates.size();
               
if (wean_dates_size > 0) {
  pigknows::Date wean_date;
  pigknows::DoubleCell dateTotals;
  // Get a baseline time (date does not matter as since it will be used )
  struct std::tm baseTime = {0,0,0,27,9,82}; /* October 27, 1982 (Zachs bday :) */
  std::time_t x = std::mktime(&baseTime);

  for(int i=0; i< wean_dates_size; ++i) {
      wean_date = bgi->wean_dates[i];
      struct std::tm b = {0,0,0,wean_date.day(),wean_date.month() - 1,wean_date.year() - 1900};
      std::time_t y = std::mktime(&b);
      double difference = std::difftime(y, x);
      dateTotals.def++;
      dateTotals.val += difference;
  }
  int avgWeanDayThousandDay = (dateTotals.val / dateTotals.def);
  baseTime.tm_sec += avgWeanDayThousandDay;
  std::mktime(&baseTime);
  bgi->avg_wean_date = pigknows::Date((baseTime.tm_year + 1900), (baseTime.tm_mon + 1), baseTime.tm_mday);
}