Expression Builder - Thinking of abandoning it in favour of the Scripting Control!

Printable View

1 Attachment(s)

Ok. Here goes. Over the past few days a couple of threads had come up looking a method by which, numerical expression in a text box and/or a string variable can be evaluated at runtime, so that users may type in text in a textbox which will then be taken as an equation for evaluation.

One of them is this. I can't seem to find the other. Seems to have been deleted.

While the Script Control does have an "Eval" method, it cannot accomodate runtime variable, something like the poster in the above link was seeking.

I have attempted a crude approximation of such an Expression Builder with a function to handle creation & storage of runtime variables to be used in that builder. The class module is attached and the sample code is listed below.

Comments, ideas, corrections, please...

Especially on how to handle BODMAS in the expression.

VB Code:

Dim myEval As New cls_Exp_Build
 
Private Sub CreateVariables()
With myEval
    .Add_New_Variable "strUserName", "String"
    .Add_New_Variable "lngScoreFirst", "Long"
    .Add_New_Variable "lngScoreSecond", "Long"
    .Add_New_Variable "lngScoreThird", "Long"
End With
End Sub
 
Private Sub SetVariables()
With myEval
    .Set_Var_Value("strUserName") = "KayJay"
    .Set_Var_Value("lngScoreFirst") = "100"
    .Set_Var_Value("lngScoreSecond") = "100"
    .Set_Var_Value("lngScoreThird") = "100"
End With
End Sub
 
Private Sub Command1_Click()
With myEval
 
MsgBox "The result of the expression " & vbCrLf & vbCrLf & _
         Text1.Text & vbCrLf & vbCrLf & _
         "is " & .Numerical_Evaluation(Text1.Text)
 
MsgBox "The average score of " & _
        .Get_Var_Value("strUserName") & _
        " is " & _
        .Numerical_Evaluation(.Get_Var_Value("lngScoreFirst") & _
        " + " & _
        .Get_Var_Value("lngScoreSecond") & _
        " + " & _
        .Get_Var_Value("lngScoreThird") & _
        " / 3")
 
MsgBox .Get_Var_Value("strUserName") & _
        "'s average score is " & _
        .Numerical_Evaluation("Avrge " & .Get_Var_Value("lngScoreFirst") & _
        "," & _
        .Get_Var_Value("lngScoreSecond") & _
        "," & _
        .Get_Var_Value("lngScoreThird"))
 
End With
 
End Sub
 
Private Sub Form_Load()
Call CreateVariables
Call SetVariables
 
Text1.Text = "lngScoreFirst + lngScoreSecond + lngScoreThird / 3"
End Sub

Jan 28th, 2003, 02:03 PM
KayJay

~Just bumping it up the list before I sign off~

Thanx to all those who have dl the Class. Expecting Ur feedback

Regards

KayJay
Jan 28th, 2003, 11:16 PM
TSur

1 Attachment(s)

KayJAy,
Thanks for your help on this. I have been trying to figure out how it all works and I understand it for the most part. But I am having problems when I put in a "(" or ")"
I think it has something to do with the first one more then the second one... Not sure what I should do.

So if I make a formula that looks like this

a = SqFt + SqFt

since SqFt = 100000
this will = 200000

But if I put this

a = ( SqFt + SqFt )
it only = 100000

it doesn't count the first SqFt.

I used the code you gave me on the other post and added my formula creator to it. Take a look when you got time and see what I need to do.

Everything else seems to work fine but that...
Jan 28th, 2003, 11:46 PM
TSur

One other thing. The user wouldn't enter in the name of the Var. on the same text line as the formula itself. The formula and the name of the Var. will be save as 2 different fields in a database. So There will be another textbox like L W and Depth that will have the name Say (varNameTxt) and when it gets tested it will use that as and not A the way it is now.

So it will be

MSGBOX varNameTxt.text & " = " & EquationResult
Jan 29th, 2003, 01:09 AM
KayJay

Tsur, I am yet to find a method of handling Brackets. BODMAS, i.e. Brackets-Of-Division-Multiplication-Addition-Subtraction. Any equation is generally evaluated in that order. If u solve the below, U'll understand what I am trying to say.

(((25 + 1/10th of 100) / 32) - 85) * 51 + 5 - 1

Need to work on that.

As to Ur seond point, I'll look it up.
Jan 29th, 2003, 04:58 AM
KayJay

Tsur, I will reply in your other thread. I would like to keep this thread for the general discussion of Expression Builders

Regards

KayJay
Jan 29th, 2003, 12:41 PM
KayJay
I have updated the Class Module in my first post. It is included in this post as well. Changes include
- Incorporated evaluation of Bracketed Expressions
- Made the operations into separate function.
- An "Average" function is included as a sample for extensibility
- Changed the name of the Exposed Function Name. Its now called "Eval"
.....
- I have added comments. :D
Comments, ideas, improvements correction? :)

Regards

KayJay
Jan 29th, 2003, 12:43 PM
KayJay

1 Attachment(s)

Sorry. The attachment
Jan 29th, 2003, 01:20 PM
techgnome

I still think the Scripting Control is the better way to go...... but maybe that's just me....
Jan 29th, 2003, 01:31 PM
KayJay

Techgnome: U answered my question before I could ask. (in the other thread). Thanx. Did not know that was possible with the Script control.
Jan 29th, 2003, 01:40 PM
techgnome

Quote:

Originally posted by KayJay
Techgnome: U answered my question before I could ask. (in the other thread). Thanx. Did not know that was possible with the Script control.

I'm psycedellic like that... ;)
Jan 29th, 2003, 01:48 PM
TSur

I had an idea about the "("

Say the textbox was this:

SfFt = 4

( SqFt *2000 ) / 2

What if you used an If- Then with the "("

So it will search for the first "(" then the next ")" and it will pull all the text info between the ( ) and then take what was left from the text and do the math.

So it would just take and figure this out

SqFt *2000 = 8000

and it would hold 8000 in a Var. and then add the 2 varables together for this:

8000 / 2

What else I thought was what if this was a formula: So more then one set of "()"

( SqFt * 2 - (1000 - 50 ) )

IT would have to search for “(“ but if the next one was a “(“ then it would need to keep searching tell if found the following “)” and take that out first and do that.

So it would first have to pull this

( 1000 - 50 ) and do that then it would leave

So you would be left with 950

- ( SqFt * 2 )

then it would need to be in a loop so it searches to see if there are any "(" left and if so pull them out and do the equation that is in the middle.

Then this would be 8

So it would be 8 – 950

So the answer would be -942

This was just something I thought of while I was trying to sleep. I don’t know how I would go about adding it to your code… Maybe you can do something with this or at least get a idea from mine…
Jan 29th, 2003, 01:55 PM
KayJay

I've already done that in the Class, TSur. ;)

Technome: U meant psychic, right?
Jan 29th, 2003, 02:05 PM
techgnome

KJ: yesno.... it was meant to be a play on words....
Jan 29th, 2003, 02:09 PM
KayJay

:cool: :cool:

U must be in Ur 50s if Ur still into "Psycedellic". :p . Jus' kidding!

Thanx for the info on the Scripting Control pal. Cheers and Good Luck

Regards

KayJay
Jan 29th, 2003, 02:15 PM
techgnome

Quote:

Originally posted by KayJay
:cool: :cool:
U must be in Ur 50s if Ur still into "Psycedellic". :p . Jus' kidding!
KayJay

Oh God, no, please don't make me old than I really am.... I'm justnow turning 30 (next week) as it is..... still got a ways to get to 50!..... ;)
Jan 29th, 2003, 03:44 PM
TSur

KayJay - How would I use your class in my program? Kinda new to all this and I haven't really used classes all that much?
Jan 29th, 2003, 04:28 PM
dw85745

Stumbled across the discussion so let me put in my two cents worth.

From my knowledge there are only two solutions to the problem:

1. Prewritten functions

- use scripting or a list box which executes a self contained function which does something specific

2. Allow user to write functions

- requires a parse routine to evaluate the function and all tokens ('e.g. "(" ) contained withing the function as well as deal with any reserved words which may conflict with the compiler to be used.
- evaluated function is then compiled and called from the
main application.
Jan 30th, 2003, 01:36 AM
KayJay
Quote:

Originally posted by TSur
KayJay - How would I use your class in my program? Kinda new to all this and I haven't really used classes all that much?

The same code I posted in the first post, should give a pointer.

Create and instance of the Class. Then use the OBj.Eval function to return the result.
VB Code:
```
Dim obj As New cls_Exp_Build
 
'Usage
dim result as double
result = obj.eval("(25 + 8) * (5 * (10 / 2))")
```
Jan 30th, 2003, 01:39 AM
KayJay

Quote:

Originally posted by dw85745
Stumbled across the discussion so let me put in my two cents worth.

From my knowledge there are only two solutions to the problem:

1. Prewritten functions

- use scripting or a list box which executes a self contained function which does something specific

2. Allow user to write functions

- requires a parse routine to evaluate the function and all tokens ('e.g. "(" ) contained withing the function as well as deal with any reserved words which may conflict with the compiler to be used.
- evaluated function is then compiled and called from the
main application.

Both are precisely what the Class Module does. ;)

1) Prewritten Functions which take arguments and return result are stored in the Class Modules.

2) A parsing routine which takes a string as its argument and returns the evaluated result of that string. The string can contain Runtime created variables as well.

;)
Jan 30th, 2003, 09:36 AM
dw85745

KayJay:

Thanks for posting the class, will take an indepth look at it today.

BTW, agree with this:

"Find purpose, the means will follow"

David
Jan 30th, 2003, 04:24 PM
TSur

I am just stupid cuz I can't figure this out...

I tried to put this in with my test button but it doesn't work

Private Sub Command111_Click()
Dim NewVar As String
Dim EquationResult As Double
Dim obj As New cls_Exp_Build

Depth = 20

Assign_And_Calculate_Area Val(LengthTxt.Text), Val(WidthTxt.Text), Val(DepthTxt.Text)

EquationResult = obj.Eval(FormulaTxt.Text)
MsgBox NewVar & " = " & EquationResult

if you have a form that you made using the class that you can upload that would be helpful so I can see how you did it...
Jan 31st, 2003, 06:37 AM
KayJay

Tsur:
I've answered to Ur previous post here

dw85745: I did not say that, Mahatma Gandhi said it :)
Aug 11th, 2003, 01:03 AM
Mikey996

Hi KayJay,

I am certainly in love with your expression builder class. I got it through a friend because a firewall blocks me from downloading the cls-file (I guess you better zip your files to keep them available to anyone).

Now I was fooling around with the code and I was wondering if it would be possible to extend this class so it could read functions as well. I was thinking of evaluating expressions like:
If(Mid(txtSomeText; 3; 2) = "GE" Or dblSomeNumber >= 4; 3; 5)

You think this can be done?
Aug 11th, 2003, 06:51 AM
jian2587

For those who learnt prefix,infix and postfix in C or the like, things
like expression evaluator is a must for them to practise coding.

And if u want to read expressions as well, might as well turn it to
an interpreter;)

and KayJay, nice of u to share the codes. Will see ur codes to see
wut can I improve in my own expression evaluator.
Aug 11th, 2003, 08:37 AM
Mikey996

?:confused:

What do you mean by turning it to an interpreter
Aug 12th, 2003, 07:29 AM
jian2587

Sorry, slipped my keyboard:p
I meant, if u want to read functions(executable codes) as well,
might as well make an interpreter instead of a math expression
evaluator.
Aug 12th, 2003, 08:14 AM
Mikey996

You wouldn't know of any examples for this 'interpreter'?