#include <iostream>

using namespace std;

/*
 * This interactive C++ program determines in a year is a leap year.
 *
 * creator: g.d.thurman
 * created: 2008.02.29  [leap day of 2008]
 */
int main(int, char**) {
   int y;

   do {
      cout << "Enter a year (0 to exit): ";
      cin >> y;
      if (cin.fail()) {
         cout << "*** error:  you must enter an integer" << endl;
         return EXIT_FAILURE;
      } else if (!y)
         return EXIT_SUCCESS;
      if (y < 0) {
         cout << "negative integers are not allowed" << endl;;
         continue;
      }
     /* [source: TimeAndDate.com]
      * 1. Every year that is divisible by four is a leap year;
      * 2. of those years, if it can be divided by 100, it is NOT 
      *    a leap year, unless
      * 3. the year is divisible by 400. Then it is a leap year.
      * Note: Before 1752, all years divisible by 4 were leap years.
      */
      cout << y << " is ";
      if (y % 4)
         cout << "not ";
      else if (y >= 1752 && !(y % 100) && (y % 400)) 
         cout << "not ";
      cout << "a leap year" << endl;
   } while(y);
}