I'm using the calculate working day code from the access web website.  I want
to know how to implement the code so that it will return 0 when only one date
is passed as a parameter.

Here is the code

Public Function Workdays(ByVal dtmStart As Date, ByVal dtmEnd As Date, _
Optional adtmDates As Variant = Empty) _
As Integer


   ' Count the business days (not counting weekends/holidays) in
   ' a given date range.
   
   ' Modified from code in
   ' "Visual Basic Language Developer's Handbook"
   ' by Ken Getz and Mike Gilbert
   ' Copyright 2000; Sybex, Inc. All rights reserved.
   
   ' Requires:
   '   SkipHolidays
   '   CountHolidays
   '   IsWeekend
   
   ' In:
   '   dtmStart:
   '       Date specifying the start of the range (inclusive)
   '   dtmEnd:
   '       Date specifying the end of the range (inclusive)
   '       (dates will be swapped if out of order)
   '   adtmDates (Optional):
   '       Array containing holiday dates. Can also be a single
   '       date value.
   ' Out:
   '   Return Value:
   '       Number of working days (not counting weekends and optionally,
holidays)
   '       in the specified range.
   ' Example:
   '   Debug.Print Workdays(#7/2/2000#, #7/5/2000#, _
   '    Array(#1/1/2000#, #7/4/2000#))
   '
   '   returns 2, because 7/2/2000 is Sunday, 7/4/2000 is a holiday,
   '   leaving 7/3 and 7/5 as workdays.
   
   Dim intDays As Integer
   Dim dtmTemp As Date
   Dim intSubtract As Integer

   ' Swap the dates if necessary.>
   If dtmEnd < dtmStart Then
       dtmTemp = dtmStart
       dtmStart = dtmEnd
       dtmEnd = dtmTemp
   End If
   
   ' Get the start and end dates to be weekdays.
   dtmStart = SkipHolidaysA(adtmDates, dtmStart, 1)
   dtmEnd = SkipHolidaysA(adtmDates, dtmEnd, -1)
   
   If dtmStart > dtmEnd Then
   
       ' Sorry, no Workdays to be had. Just return 0.
       Workdays = 0
   
   ElseIf dtmStart < dtmEnd Then
       intDays = dtmEnd - dtmStart + 1
       
       ' Subtract off weekend days.  Do this by figuring out how
       ' many calendar weeks there are between the dates, and
       ' multiplying the difference by two (because there are two
       ' weekend days for each week). That is, if the difference
       ' is 0, the two days are in the same week. If the
       ' difference is 1, then we have two weekend days.
       intSubtract = (DateDiff("ww", dtmStart, dtmEnd) * 2)
       
       ' The answer to our quest is all the weekdays, minus any
       ' holidays found in the table.
       intSubtract = intSubtract + _
        CountHolidaysA(adtmDates, dtmStart, dtmEnd)
       
       Workdays = intDays - intSubtract
   
   Else
   Workdays = 0
   End If

End Function

Private Function CountHolidaysA( _
adtmDates As Variant, _
dtmStart As Date, dtmEnd As Date) As Long

   ' Count holidays between two end dates.
   '
   ' Modified from code in
   ' "Visual Basic Language Developer's Handbook"
   ' by Ken Getz and Mike Gilbert
   ' Copyright 2000; Sybex, Inc. All rights reserved.
   
   ' Required by:
   '   dhCountWorkdays
   
   ' Requires:
   '   IsWeekend
   
   
   Dim lngItem As Long
   Dim lngCount As Long
   Dim blnFound As Long
   Dim dtmTemp As Date
   
   On Error GoTo HandleErr
   lngCount = 0
   Select Case VarType(adtmDates)
       Case vbArray + vbDate, vbArray + vbVariant
           ' You got an array of variants, or of dates.
           ' Loop through, looking for non-weekend values
           ' between the two endpoints.
           For lngItem = LBound(adtmDates) To UBound(adtmDates)
               dtmTemp = adtmDates(lngItem)
               If dtmTemp >= dtmStart And dtmTemp <= dtmEnd Then
                   If Not IsWeekend(dtmTemp) Then
                       lngCount = lngCount + 1
                   End If
               End If
           Next lngItem
       Case vbDate
           ' You got one date. So see if it's a non-weekend
           ' date between the two endpoints.
           If adtmDates >= dtmStart And adtmDates <= dtmEnd Then
               If Not IsWeekend(adtmDates) Then
                   lngCount = 1
               End If
           End If
   End Select

ExitHere:
   CountHolidaysA = lngCount
   Exit Function
   
HandleErr:
   ' No matter what the error, just
   ' return without complaining.
   ' The worst that could happen is that the code
   ' include a holiday as a real day, even if
   ' it's in the table.
   Resume ExitHere
   
 
End Function

Private Function FindItemInArray(varItemToFind As Variant, _
avarItemsToSearch As Variant) As Boolean
   Dim lngItem As Long
   
   On Error GoTo HandleErrors
   
   For lngItem = LBound(avarItemsToSearch) To UBound(avarItemsToSearch)
       If avarItemsToSearch(lngItem) = varItemToFind Then
           FindItemInArray = True
           GoTo ExitHere
       End If
   Next lngItem
   
ExitHere:
   Exit Function
   
HandleErrors:
   ' Do nothing at all.
   ' Return False.
   Resume ExitHere
End Function

Private Function IsWeekend(dtmTemp As Variant) As Boolean
   ' If your weekends aren't Saturday (day 7) and Sunday (day 1),
   ' change this routine to return True for whatever days
   ' you DO treat as weekend days.
   
   ' Modified from code in "Visual Basic Language Developer's Handbook"
   ' by Ken Getz and Mike Gilbert
   ' Copyright 2000; Sybex, Inc. All rights reserved.
   
   ' Required by:
   '   SkipHolidays
   '   dhFirstWorkdayInMonth
   '   dbLastWorkdayInMonth
   '   dhNextWorkday
   '   dhPreviousWorkday
   '   dhCountWorkdays
   
   If VarType(dtmTemp) = vbDate Then
       Select Case Weekday(dtmTemp)
           Case vbSaturday, vbSunday
               IsWeekend = True
           Case Else
               IsWeekend = False
       End Select
   End If
End Function

Private Function SkipHolidaysA( _
adtmDates As Variant, _
dtmTemp As Date, intIncrement As Integer) As Date
   ' Skip weekend days, and holidays in the array referred to by adtmDates.
   ' Return dtmTemp + as many days as it takes to get to a day that's not
   ' a holiday or weekend.
   
   ' Modified from code in
   ' "Visual Basic Language Developer's Handbook"
   ' by Ken Getz and Mike Gilbert
   ' Copyright 2000; Sybex, Inc. All rights reserved.
   
   ' Required by:
   '   dhFirstWorkdayInMonthA
   '   dbLastWorkdayInMonthA
   '   dhNextWorkdayA
   '   dhPreviousWorkdayA
   '   dhCountWorkdaysA
   
   ' Requires:
   '   IsWeekend
   
   Dim strCriteria As String
   Dim strFieldName As String
   Dim lngItem As Long
   Dim blnFound As Boolean
   
   On Error GoTo HandleErrors
   
   ' Move up to the first Monday/last Friday, if the first/last
   ' of the month was a weekend date. Then skip holidays.
   ' Repeat this entire process until you get to a weekday.
   ' Unless adtmDates an item for every day in the year (!)
   ' this should finally converge on a weekday.
   
   Do
       Do While IsWeekend(dtmTemp)
           dtmTemp = dtmTemp + intIncrement
       Loop
       Select Case VarType(adtmDates)
           Case vbArray + vbDate, vbArray + vbVariant
               Do
                   blnFound = FindItemInArray(dtmTemp, adtmDates)
                   If blnFound Then
                       dtmTemp = dtmTemp + intIncrement
                   End If
               Loop Until Not blnFound
           Case vbDate
               If dtmTemp = adtmDates Then
                   dtmTemp = dtmTemp + intIncrement
               End If
       End Select
   Loop Until Not IsWeekend(dtmTemp)
   
ExitHere:
   SkipHolidaysA = dtmTemp
   Exit Function
   
HandleErrors:
   ' No matter what the error, just
   ' return without complaining.
   ' The worst that could happen is that we
   ' include a holiday as a real day, even if
   ' it's in the array.
   
   Resume ExitHere
End Function