Generating Unique Numbers for Worksheets

Sometimes you may need Excel to generate a unique number for your worksheets. For instance, you could be using Excel to create forms such as invoices, statements, or tracking sheets, and you need unique numbers for each form (I'll call this a ticket number). This, of course, implies that Excel needs to remember the number from one session to the next.

There are a couple of ways you can approach this problem. If the numbers don't need to be sequential, you could create a ticket number based on the current time of day, in seconds. The following macro can be added to the ThisWorksheet object:

Private Sub Workbook_NewSheet(ByVal Sh As Object)
    Dim lTicket As Long
    lTicket = CLng(Time * 24 * 60 * 60)
    Sh.Range("A1") = lTicket
End Sub

The macro is triggered every time a new worksheet is added to the workbook. It takes the current time, converts it to an integer number of seconds, and then places that value into cell A1. The likelihood of duplicating ticket numbers within any given day is remote, but it could happen over time. (For instance, if you create a ticket at the exact same time today that you did yesterday or last week.)

To get around this problem, you could create a ticket number in the following manner:

Private Sub Workbook_NewSheet(ByVal Sh As Object)
    Dim sTemp As String
    sTemp = Format(Date, "yymmdd") & Format(Time, "hhmmss")
    Sh.Range("A1") = sTemp
End Sub

This version of the event handler constructs a ticket number based both the date and time. Unless you are creating tickets very quickly, this approach should reduce the possibility of duplicate numbers generated by the macro.

If the numbers must be sequential within the current workbook, then you can define a name that contains the current high value of your ticket number, and then a macro that places that number in a cell on a new worksheet and increments the value of the stored number. Follow these steps to start:

1. Choose Name from the Insert menu, then choose Define. Excel displays the Define Name dialog box. (See Figure 1.)



Figure 1. The Define Name dialog box.

2. In the Name box, enter a name such as MaxNum.
3. In the Refers To area at the bottom of the dialog box, enter an equal sign followed by the value you want used for the next ticket number.
4. Click on OK. The new name is stored in the workbook.

Now, add the following macro to the ThisWorksheet object in the VBA Editor:

Private Sub Workbook_NewSheet(ByVal Sh As Object)
    Dim iMax As Integer
    iMax = Mid(ThisWorkbook.Names("MaxNum"), 2)
    Sh.Range("A1") = iMax
    iMax = iMax + 1
    ThisWorkbook.Names("MaxNum").RefersTo = "=" & iMax
End Sub

This macro is executed every time you insert a new worksheet in the workbook. It retrieves the value you stored in the MaxNum, places that value into cell A1 of the new worksheet, and then increments what is stored in MaxNum.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (3336) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Generating Unique Numbers for Worksheets.