// Code derived from Stroustrup's PPP2 book
// § 9.5 Enumerations
//  -and beginning on p 318

#include <iostream>
#include <stdexcept>

using namespace std;

void error(const char* s) { throw runtime_error(s); }

enum class Month {
  jan = 1,
  feb,
  mar,
  apr,
  may,
  jun,
  jul,
  aug,
  sep,
  oct,
  nov,
  dec
};

enum class Day {
  monday,
  tuesday,
  wednesday,
  thursday,
  friday,
  saturday,
  sunday
};

Month int_to_month(int x)
{
  if (x < int(Month::jan) || int(Month::dec) < x)
    error("bad month");

  return Month{x};
}

void f(int m)
{
  [[maybe_unused]] Month mm = int_to_month(m);

  // ...
}

int main()
try {
  [[maybe_unused]] Month m = Month::feb;

  // Month m2  = feb;       // error: feb is not in scope
  // m         = 7;         // error: can’t assign an int to a Month
  // int   n   = m;         // error: can’t assign a Month to an int

  [[maybe_unused]] Month mm = Month(7);  // convert int to Month (unchecked)

  // Month bad = 9999;      // error: can’t convert an int to a Month

  f(4);
  f(99);  // run-time error: bad month

} catch (exception& e) {
  cerr << "error: " << e.what() << '\n';
  return 1;

} catch (...) {
  cerr << "Oops: unknown exception!\n";
  return 2;
}