Q159974: HOWTO: Evaluate Numeric Expressions Stored as a String

Article: Q159974
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0
Operating System(s): 
Keyword(s): kbprogramming kbVBp400
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
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SUMMARY
=======

Given a string expression, the Val function returns the number contained in that
string. However, if it encounters a character that is not a number or part of a
number, it ignores the rest of the string. For example, Val("2") returns the
number 2, but Val("2+2") also returns the number 2, and Val("(2+2)") returns the
number 0.

This article describes how to obtain the actual value of a numeric expression
that is stored as a String by using the existing features in the Excel Object
Model.

MORE INFORMATION
================

In some instances, you might want to allow users to type in their own numeric
expression in a TextBox and then evaluate it. In other cases, it might be
necessary to read an ASCII file that contains a series of numeric expressions
and then produce another ASCII file containing the results of those expressions.
If this is the only purpose of your Visual Basic application, it is probably
best, for speed and efficiency, to write a parser. However, for a simple and
quick solution, you can use OLE Automation and the Excel Object Library to
accomplish these tasks.

Step-by-Step Example
--------------------

1. Start a new project in Visual Basic. Form1 is created by default.

2. Add a TextBox and a CommandButton to Form1.

3. Set the Text property of the TextBox to "".

4. Set the Caption property of the CommandButton to "Evaluate."

5. Add the following code to the Click event of the CommandButton:

        Private Sub Command1_Click()
            MsgBox MyVal(Text1.Text)
        End Sub

6. Add the following code to the General Declarations section of Form1:

        Private Function MyVal(s As String) As Double
        Dim xl As Object

            Set xl = CreateObject("excel.application")
            xl.Workbooks.Add

            xl.ActiveCell.Formula = "=" & s
            MyVal = xl.ActiveCell.Value

            xl.ActiveWorkbook.Close savechanges:=False
            xl.Quit
            Set xl = Nothing

        End Function

7. Run the project by pressing the F5 key. Type a valid numeric expression in
  the TextBox and click the CommandButton to evaluate the expression.

Additional query words:

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Keywords          : kbprogramming kbVBp400 
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Version           : WINDOWS:4.0
Issue type        : kbhowto

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