I use UserForms almost exclusively for supplying input data to my
Excel programs. I permit users to enter the numerical data in the
respective textboxes in virtually any formatted or algebraic form,
such as $12,345,678 or $12.345*(1.035)^2.5-10500/2

The ability to modify the data algebraically lets users pose
"What If?" questions without having to find their hand
calculators and avoids transcription errors. I also wanted
to trap an incorrect symbol that is inadvertently entered
by the user.

Several MVP's (particularly Melanie B.) supplied insightful
help, and I would like to post the finished procedure for
anyone who's interested. If any of you MVP's believe it
worthy enough, you can pass it up to one of the Excel
web sites that catalog novel procedures.

-- Dennis Eisen

In the code for each texbox insert:

Private Sub MyTextBox_AfterUpdate()
Dim ResultString As Variant
ResultString = Algebra(MyUserForm.MyTextBox.Text)
MyUserForm.MyTextBox.Text = Format(ResultString, "$###,###,##0")
'Replace $###,###,###0 by whatever format each input requires
End Sub


In the main module code insert:

Function Algebra(InputString As String) As Variant
If InputString Like "*[!0-9$.,+-/*^()]*" Then
'The ! right after [ serves as the negation operator
Dim Message As String
Message = "Sorry, the input field you just left contains one or more illegal
characters."
MsgBox Message, 48, "Data Entry Error"
Algebra = InputString
Exit Function
End If
Algebra = InputString
If InputString Like "*[+-/*^()]*" Then
InputString = Replace(InputString, "$", "")
InputString = Replace(InputString, ",", "")
Algebra = Evaluate(InputString)
End If
If Algebra = "" Then Algebra = 0
End Function