/** @file list4307.cpp */
/** Listing 43-7. Checking for a Zero Denominator in reduce() */
void rational::reduce()
{
  if (denominator_ == 0)
    throw zero_denominator("denominator is zero");
  if (denominator_ < 0)
  {
    denominator_ = -denominator_;
    numerator_ = -numerator_;
  }
  int div(gcd(numerator_, denominator_));
  numerator_ = numerator_ / div;
  denominator_ = denominator_ / div;
}