Calculating mathematical formulas

[Ronald Weber]

I'm looking to calculate math formulas as follows:

F = "34 + 62 * 10 - 2"

X = SomeFunction(F)

X would contain the value 652

Is there such a function?

Thanks, Ron

[Cecil Williams]

Ron,

Could you be a little more explicit? I presume you want to pass
a string value to function 'SomeFunction(F)' and expect a
number value in return.

Does this setup always correspond to the exact same sequence
ie ("A + B * C - D") or could it be different based upon the string passed, ie ("A * B - C + D") or something like that.

To answer your question, I know of "NO" standard basic function
that does this. Would require custom parsing of string and performing whatever action is required.

Cecil

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[James GrahamEagle]

Look at Gafny Jacob's "Evaluate math expression" thread in the
source code section.

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[Ronald Weber]

I'm looking to evaluate any formula I enter. I'm creating a VB app that has fields that accept formulas like an Excel cell would. I just want it to be able to perform your basic math operations along with parentheses.

Thanks, Ron

Originally posted by Cecil Williams:
Ron,

Could you be a little more explicit? I presume you want to pass
a string value to function 'SomeFunction(F)' and expect a
number value in return.

Does this setup always correspond to the exact same sequence
ie ("A + B * C - D") or could it be different based upon the string passed, ie ("A * B - C + D") or something like that.

To answer your question, I know of "NO" standard basic function
that does this. Would require custom parsing of string and performing whatever action is required.

Cecil

------------------

[Jeffrey R. Radue]

Ronald,

Quinn Tyler Jackson has provided a algebraic solver package which compiles in PB. The code is public domain on the ABC web site. Check out his URL http://www.qtj.net/~quinn/ for more info. It is an elegant piece of work.

Jeff

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[ShirlunTse]

Hi,

We have a lib program doing this function, the current version
is for PDS, but we can port to PBDLL about few days and provide
compiled DLL version.

Are you interested?

mailto:[email protected][email protected]</A>


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[Ronald Weber]

Below is a VB app I created to handle simple formulas. It shouldn't take much to convert it to a PBDLL and I'll post it again when I do this myself. It handles the following operators: + - * / ^ ( ). Make sure the operators and numbers are separated by a space. It needs to be cleaned up but it's a good start. The VB objects are defined below:

txtFormula.text = text box that accepts the formula
cmdCalculate_Click = command button method to calculate the value.
value = subroutine to calculate math functions without parentheses.
lblResult.caption = label that is set to the final value.

The program starts at the highest level parentheses and calculates the contents. It recreates the formula by calculating the formula within the pars and removing the pars. This process is repeated until the formula is a single value without parenthesis.

Thanks for all the help, Ron

Private Sub cmdCalculate_Click()
 
    Dim c As String
    Dim f As String
    Dim i As Integer
    Dim ii As Integer
    Dim lev As Integer
    Dim parmaxlev As Integer
    Dim parcount As Integer
    Dim pars(100, 3) As String
     
    f = txtFormula.Text
     
again:
     
    ' Locate pars.
    lev = 0
    parcount = 0
    parmaxlev = 0
    For i = 1 To Len(f)
     
        c = Mid(f, i, 1)
        If c = "(" Then
            lev = lev + 1
            parcount = parcount + 1
            If lev > parmaxlev Then parmaxlev = lev
            pars(parcount, 1) = c
            pars(parcount, 2) = Str(lev)
            pars(parcount, 3) = Str(i)
        End If
        If c = ")" Then
            parcount = parcount + 1
            pars(parcount, 1) = c
            pars(parcount, 2) = Str(lev)
            pars(parcount, 3) = Str(i)
            lev = lev - 1
        End If
     
    Next i
     
    ' Simplify formula.
    For i = parmaxlev To 1 Step -1
     
        For ii = 1 To parcount
         
            If pars(ii, 1) = "(" And Val(pars(ii, 2)) = i Then
             
                c = Mid(f, Val(pars(ii, 3)) + 1, Val(pars(ii + 1, 3) - Val(pars(ii, 3)) - 1))
             
                Call value(c)
                 
                f = Left(f, Val(pars(ii, 3)) - 1) + c + Right(f, Len(f) - Val(pars(ii + 1, 3)))
             
                GoTo again
            
            End If
    
        Next ii
    
    Next i
    
    Call value(f)
    
    lblResult.Caption = f
    
    MsgBox "Formula Calculated"
 
End Sub
 
Private Sub value(f As String)
 
    Dim c As String
    Dim cl As String
    Dim i As Integer
    Dim ii As Integer
    Dim param(100) As String
    Dim params As Integer
 
    f = LTrim(RTrim(f))
     
again:
 
    If f <> "" Then
     
        ' Get formula parameters.
        params = 1
        For i = 1 To Len(f)
        
            cl = c
            c = Mid(f, i, 1)
            
            If c <> " " Then
            
                param(params) = param(params) + c
                
            End If
            If c = " " And cl <> " " Then
            
                params = params + 1
                param(params) = ""
                
            End If
            
        Next i
        
        ' Raise number to a power.
        For i = 1 To params
        
            If param(i) = "^" Then
                param(i) = Val(param(i - 1)) ^ Val(param(i + 1))
                param(i - 1) = ""
                param(i + 1) = ""
                f = ""
                For ii = 1 To params
                    f = f + " " + param(ii)
                Next ii
                GoTo again
            End If
            
        Next i
        
        ' Multiply or divide numbers.
        For i = 1 To params
        
            If param(i) = "*" Then
                param(i) = Val(param(i - 1)) * Val(param(i + 1))
                param(i - 1) = ""
                param(i + 1) = ""
                f = ""
                For ii = 1 To params
                    f = f + " " + param(ii)
                Next ii
                GoTo again
            End If
            If param(i) = "/" Then
                param(i) = Val(param(i - 1)) / Val(param(i + 1))
                param(i - 1) = ""
                param(i + 1) = ""
                f = ""
                For ii = 1 To params
                    f = f + " " + param(ii)
                Next ii
                GoTo again
            End If
            
        Next i
        
        ' Add or subtract numbers.
        For i = 1 To params
        
            If param(i) = "+" Then
                param(i) = Val(param(i - 1)) + Val(param(i + 1))
                param(i - 1) = ""
                param(i + 1) = ""
                f = ""
                For ii = 1 To params
                    f = f + " " + param(ii)
                Next ii
                GoTo again
            End If
            If param(i) = "-" Then
                param(i) = Val(param(i - 1)) - Val(param(i + 1))
                param(i - 1) = ""
                param(i + 1) = ""
                f = ""
                For ii = 1 To params
                    f = f + " " + param(ii)
                Next ii
                GoTo again
            End If
            
        Next i
        
    End If
     
End Sub

[Daniel Corbier]

Yes, there is a component that will allow you to do this. Visit http://www.ucalc.com and download a copy of UCalc Fast Math Parser. It includes direct support for PowerBASIC.

Daniel Corbier, UCALC