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Work Days Between Two Dates Without Cycling Through Dates

10.13.2005
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        I was thinking about how to optimize figuring out the work days between two dates and came up with this function.  It doesn't take into account holidays.  You would have to take out the workdays for holidays from the number if you want to take into account holidays, but that should be easy enough.

4GL Version
 
# workdays
# returns the number of working days between two dates
FUNCTION workdays( dt_begin, dt_end )

DEFINE
   dt_begin             DATE,
   dt_end               DATE,
   dt_first_sunday      DATE,
   dt_last_saturday     DATE,
   int_workdays         INTEGER

   # get first sunday
   LET dt_first_sunday = dt_begin + ((7 - WEEKDAY(dt_begin)) MOD 7)

   # get last saturday
   LET dt_last_saturday = dt_end + ((-1 * (WEEKDAY(dt_end) + 1)) MOD 7)

   # get work weeks between first sunday and last saturday
   LET int_workdays = (((dt_last_saturday - dt_first_sunday) + 1) / 7) * 5
   
   # if first sunday is not begin date
   IF dt_first_sunday <> dt_begin THEN

      # assume first sunday is after begin date
      # add workdays from begin date to first sunday
      LET int_workdays = int_workdays + (6 - WEEKDAY(dt_begin))

   END IF

   # if last saturday is not end date
   IF dt_last_saturday <> dt_end THEN

      # assume last saturday is before end date
      # add workdays from last saturday to end date
      LET int_workdays = int_workdays + WEEKDAY(dt_end)  
  
   END IF

   # return working days
   RETURN int_workdays

END FUNCTION

VBA Version
' WorkDays
' returns the number of working days between two dates
Public Function WorkDays(ByVal dtBegin As Date, ByVal dtEnd As Date) As Long

   Dim dtFirstSunday As Date
   Dim dtLastSaturday As Date
   Dim lngWorkDays As Long

   ' get first sunday in range
   dtFirstSunday = dtBegin + ((8 - Weekday(dtBegin)) Mod 7)

   ' get last saturday in range
   dtLastSaturday = dtEnd - (Weekday(dtEnd) Mod 7)

   ' get work days between first sunday and last saturday
   lngWorkDays = (((dtLastSaturday - dtFirstSunday) + 1) / 7) * 5

   ' if first sunday is not begin date
   If dtFirstSunday <> dtBegin Then

      ' assume first sunday is after begin date
      ' add workdays from begin date to first sunday
      lngWorkDays = lngWorkDays + (7 - Weekday(dtBegin))

   End If

   ' if last saturday is not end date
   If dtLastSaturday <> dtEnd Then

      ' assume last saturday is before end date
      ' add workdays from last saturday to end date
      lngWorkDays = lngWorkDays + (Weekday(dtEnd) - 1)

   End If

   ' return working days
   WorkDays = lngWorkDays

End Function