weekends: procedure options (main); /* 28/11/2011 */
   declare tally fixed initial (0);
   declare (d, dend, dn) fixed (10);
   declare (date_start, date_end) picture '99999999';
   declare Leap fixed (1);

   date_start = '01011900';
   do date_start = date_start to '01012100';
      d        = days(date_start, 'DDMMYYYY');
      date_end = date_start + 30110000;
      dend     = days(date_end,   'DDMMYYYY');
      Leap     = dend-d-364;
      do dn = d, d+59+Leap, d+120+Leap, d+181+Leap, d+212+Leap,
                 d+273+Leap, d+334+Leap;
         if weekday(dn) = 6 then
            do;
               put skip list (daystodate(dn, 'MmmYYYY') || ' has 5 weekends' );
               tally = tally + 1;
            end;
      end;
   end;

   put skip list ('Total number of months having 3-day weekends =', tally);

end weekends;