rtn checksum in c++

rtn_checksum.cc

bool rtn_checksum(const std::string& routing_number) {
  std::vector<int> const multipliers{3, 7, 1, 3, 7, 1, 3, 7, 1};

  auto to_int = [](char c) { return std::stoul(&c, nullptr, 10); };
  auto const routing_digits = routing_number | views::transform(to_int);

  auto multiply = [](auto a, auto b) { return a * b; };
  auto sum =
      accumulate(views::zip_with(multiply, routing_digits, multipliers), 0);

  return sum % 10 == 0;
}