#include <library.h>

bool is_leap_year(const int Y)
{ if (Y % 400 == 0)
    return true;
  if (Y % 100 == 0)
    return false;
  if (Y % 4 == 0)
    return true;
  return false; }

int days_in_month(const int M, const int Y)
{ if (M == 1 || M == 3 || M == 5 || M == 7 || M == 8 || M == 10 || M == 12)
    return 31;
  if (M == 2)
  { if (is_leap_year(Y))
      return 29;
    else
      return 28; }
  if (M == 4 || M == 6 || M == 9 || M == 11)
    return 30;
  cout << "M=" << M << " is invalid for days_in_month\n";
  exit(1); }

void test()
{ cout << "Enter month and year: ";
  const int month = read_int();
  const int year = read_int();
  cout << "There are " << days_in_month(month, year) << " days in that month\n";
  test(); }

int main()
{ test(); }