yep fair enough, I see it now

std::string Currency::formatAmount(uint64_t amount) const {
  std::string s = std::to_string(amount);
  if (s.size() < m_numberOfDecimalPlaces + 1) {
    s.insert(0, m_numberOfDecimalPlaces + 1 - s.size(), '0');
  }
  s.insert(s.size() - m_numberOfDecimalPlaces, ".");
  return s;
}