Dynamically Evaluating Expressions in vb6

[jfg]

Folks,

Does anybody know how I can dynamically evaluate a maths expression that is held in a string.

i.e.

text1="10/3"
ans = eval(text1)
'ans is now 3.3333

The eval function works in ASP 3.0 but doesn't work with vb6 is there an equivalent function I can use in vb?

note: I' dont have ASP 3.0 so I can't include a reference.

Cheers
John

[HeSaidJoe]

[code]
Private Sub Command1_Click()
'don't use the quotes ["10/3"]
Text1 = 10 / 3
MsgBox Val(Text1)
End Sub
[code]

[jfg]

oops

Sorry HeSaidJoe, but I just put in the line
text1="10/3"
as an example
text1 is a text box that can be edited so I don't know whats going to be in there hence

ans = eval(text1.text)

if I just use val(text1.text) and text1="10/3" then I get an answer of 10 !!!!

John

[Iain17]

This is actually a very tough question, and the code to go behind it all will be quite complicated. You see, to do it properly you have to take into account Brackets and operator precedence. You then have to do the right calculation on each pair of operators, unless it is a maths function that takes one operator, and work out the result. Harder than it sounds at first.

Good Luck!

[jfg]

Iain17

I know what you mean, this would involve some mental recursion and some form of stack data structure. I was kinda hoping for a function (in a dll or somewhere) along the lines of ASP 3.0's eval or execute function.

John

[Sam Finch]

Alternitivley use the Microsoft Scripting Control (Goto the Project menu, hit components and select the Microsoft Script Control)

Add the new control to your form, and add this code

Private Sub Command1_Click
MsgBox ScriptControl1.Eval("3/6")
End Sub

Tada

[jfg]

Sam F,

No Joy, I don't seem to have the Microsoft Scripting Control on my system (not in components) there is a Ms Scripting runtime dll in the references but that has no eval fuction (searched with object browser).

Do you have win2000 or iis v5 on your system?

I'll have a look on msdn.microsoft for the Scripting Control, I have iexplorer v5 you'd think that would install it.

Cheers
John

[Sam Finch]

Bit strange, I've got Win2K but I had the scripting control under win 98 as well, in fact I'm pretty sure IE uses it, just as a check open a copy of notepad and put this in it

VERSION 5.00
Object = "{0E59F1D2-1FBE-11D0-8FF2-00A0D10038BC}#1.0#0"; "msscript.ocx"
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   3195
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4680
   LinkTopic       =   "Form1"
   ScaleHeight     =   3195
   ScaleWidth      =   4680
   StartUpPosition =   3  'Windows Default
   Begin MSScriptControlCtl.ScriptControl ScriptControl1 
      Left            =   210
      Top             =   1545
      _ExtentX        =   1005
      _ExtentY        =   1005
      AllowUI         =   -1  'True
   End
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   495
      Left            =   870
      TabIndex        =   0
      Top             =   390
      Width           =   2265
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

Private Sub Command1_Click()
MsgBox ScriptControl1.Eval("3/6")
End Sub

then save it as Form1.frm and open it with VB, see If it works, if it does then it means you have the control, if not then download it from somewhere.

[jfg]

Thanks Sam

But still no go - Errors in form load refer to form.log
Like so
.....
Line 2: Could not create reference: '{0E59F1D2-1FBE-11D0-8FF2-00A0 D100 38BC}#1.0#0'.
Line 13: Class MSScriptControlCtl.ScriptControl of control ScriptControl1 was not a loaded control class.
Line 16: The property name _ExtentX in ScriptControl1 is invalid.
Line 17: The property name _ExtentY in ScriptControl1 is invalid.
Line 18: The property name AllowUI in ScriptControl1 is invalid.
......

Obviously No control

I'm using NT Server 4 -SP5 IIS4
I think there is an upgrade to IIS5 which should have it.
Strangly I have the regular expression object on my system which is supposed to be part of IIS5 ??

But like you I thought ie5 would install it.

Cheers
John

[Iain17]

Sam,

Well i'll be god damned. I wish someone had told me about that about 8 months ago when i asked.

Anyway, thanks for pointing that out.