this function will calculate a string formula which support cos, sin, log, abs, mod, and example : [10*2+(2+3)]/(5 mod 4) and you will get the answer, and this function it really easy to plugin with you code.

' Programming by Visal .In
' Email : invisal@gmail.com
'
' if you like my code please vote for me in PSCODE
' here the link
' http://www.pscode.com/vb/scripts/showcode.asp?txtCodeId=59600&lngWId=1

Function Calc(exp As String) As Double

    'start searching for ()
    'everything between "(" and ")"
    'will calculate first
    
    Dim startpos As Integer
    Dim Count As Integer
    
    Dim lexp As String ' left expression
    Dim rexp As String ' right expression
    
    Dim cmid As String
    
    Dim exp2 As String
    Dim answer2 As Double
    
    ' \ and / are same division
    exp = Replace(exp, "\", "/")
    ' "[" and "(" are the same also "]" and ")"
    exp = Replace(exp, "[", "(")
    exp = Replace(exp, "]", ")")
    
    startpos = InStr(1, exp, "(")
    
    'we have found "("
    If startpos > 0 Then
        'searching for ")"

        For endpos = (startpos + 1) To Len(exp)
            Select Case Mid(exp, endpos, 1)
                Case "("
                    Count = Count + 1
                Case ")"
                    If Count = 0 Then Exit For
                    Count = Count - 1
            End Select
        Next endpos
        
        ' if there no ")" we will create ")" automatic
        If Count > 0 Then
            exp = exp & Replace(Space(Count + 1), " ", ")")
            endpos = endpos + Count
            
        End If
        
        ' check if () is empty or not
        If endpos <= startpos + 1 Then
            ' if it empty it mean 0
            exp2 = "0"
            exp2 = Replace(exp, "()", "0")
        Else
            ' get expression between "(" and ")"
            exp2 = Mid(exp, startpos + 1, endpos - (startpos + 1))
            
            ' calculate expression between "(" and ")"
            answer2 = Calc(exp2)
            
            ' replace the expression between "(" and ")"
            ' with the result that we have calculate
            exp2 = Replace(exp, "(" & exp2 & ")", answer2)
        End If
        
        Calc = Calc(exp2)
        
        Exit Function
        
    ElseIf InStr(1, exp, "abs", vbTextCompare) > 0 Then
    
        ' get absolute start position
        startpos = InStr(1, exp, "abs", vbTextCompare)
        ' clear all the text in exp2
        exp2 = ""
        
        ' get number
        For endpos = startpos + 3 To Len(exp)
            cmid = Mid(exp, endpos, 1)
            If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
                exp2 = exp2 & cmid
            Else
                Exit For
            End If
        Next endpos
        
        If exp2 <> "" Then
            ' convert it into absolute
            answer2 = Abs(CDbl(exp2))
            
            ' replace the adsolute number with the answer
            exp2 = Replace(exp, "abs" & exp2, answer2)
            Calc = Calc(exp2)
        Else
            Mid(exp, startpos, 3) = "000"
            Calc = Calc(exp)
        End If
        
        Exit Function
        
    ElseIf InStr(1, exp, "cos", vbTextCompare) > 0 Then
    
        ' get cosines start position
        startpos = InStr(1, exp, "cos", vbTextCompare)
        ' clear all the text in exp2
        exp2 = ""
        
        ' get cosines angle
        For endpos = startpos + 3 To Len(exp)
            cmid = Mid(exp, endpos, 1)
            If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
                exp2 = exp2 & cmid
            Else
                Exit For
            End If
        Next endpos
        
        If exp2 <> "" Then
            ' calculate cosines
            answer2 = Cos(CDbl(exp2))
            
            ' replace cosines with the answer
            exp2 = Replace(exp, "cos" & exp2, answer2)
            Calc = Calc(exp2)
        Else
            Mid(exp, startpos, 3) = "000"
            Calc = Calc(exp)
        End If
        
        Exit Function
        
    ElseIf InStr(1, exp, "sin", vbTextCompare) > 0 Then
    
        ' get sines start position
        startpos = InStr(1, exp, "sin", vbTextCompare)
        ' clear all the text in exp2
        exp2 = ""
        
        ' get sines angle
        For endpos = startpos + 3 To Len(exp)
            cmid = Mid(exp, endpos, 1)
            If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
                exp2 = exp2 & cmid
            Else
                Exit For
            End If
        Next endpos
        
        If exp2 <> "" Then
            ' calculate sines
            answer2 = Sin(CDbl(exp2))
            
            ' replace cosines with the answer
            exp2 = Replace(exp, "sin" & exp2, answer2)
            Calc = Calc(exp2)
        Else
            Mid(exp, startpos, 3) = "000"
            Calc = Calc(exp)
        End If
        
        Exit Function
        
    ElseIf InStr(1, exp, "log", vbTextCompare) > 0 Then
    
        ' get logarithmic start position
        startpos = InStr(1, exp, "log", vbTextCompare)
        ' clear all the text in exp2
        exp2 = ""
        
        ' get number
        For endpos = startpos + 3 To Len(exp)
            cmid = Mid(exp, endpos, 1)
            If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
                exp2 = exp2 & cmid
            Else
                Exit For
            End If
        Next endpos
        
        If exp2 <> "" Then
            ' calculate logarithmic
            answer2 = Log(CDbl(exp2))
            
            ' replace logarithmic with the answer
            exp2 = Replace(exp, "log" & exp2, answer2)
            Calc = Calc(exp2)
        Else
            Mid(exp, startpos, 3) = "000"
            Calc = Calc(exp)
        End If
        
        Exit Function
        
    ElseIf InStr(1, exp, "mod") > 1 Then
        
        ' modulo
        
        startpos = InStr(1, exp, "mod")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - (startpos + 2))
        
        Calc = Calc(lexp) Mod Calc(rexp)
        
        Exit Function
        
    ElseIf InStr(1, exp, "+") > 1 Then
        
        ' addition
        
        startpos = InStr(1, exp, "+")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - startpos)
        
        Calc = Calc(lexp) + Calc(rexp)
        
        Exit Function
        
    ElseIf InStr(1, exp, "-") > 1 Then
        
        ' subtract
        
        startpos = InStr(1, exp, "+")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - startpos)
        
        Calc = Calc(lexp) - Calc(rexp)
        
        Exit Function
        
    ElseIf InStr(1, exp, "*") > 1 Then
        
        ' multiply
        
        startpos = InStr(1, exp, "*")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - startpos)
        
        Calc = Calc(lexp) * Calc(rexp)
        
        Exit Function
        
    ElseIf InStr(1, exp, "/") > 1 Then
        
        ' divide
        
        startpos = InStr(1, exp, "/")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - startpos)
        
        answer2 = Calc(rexp)
        If answer2 = 0 Then answer2 = 1
        
        Calc = Calc(lexp) / answer2
        
        Exit Function
        
    ElseIf InStr(1, exp, "^") > 1 Then
        
        ' exponent
        
        startpos = InStr(1, exp, "^")
        lexp = Left(exp, startpos - 1)
        rexp = Right(exp, Len(exp) - startpos)
        
        Calc = Calc(lexp) ^ Calc(rexp)
        
        Exit Function

    Else
        
        If IsNumeric(exp) = True Then
            Calc = CDbl(exp)
        Else
            Calc = 0
        End If
        Exit Function
        
    End If

End Function

Hello!
Does it really work?!
your source code is very LONG!
in here, use "select case" is better than "Ifelse"
I plan to learn API, I don't know about this site alot! hopes could help me.
be successful!
Miss.Samane:)

Dosen't work with Visual Basic 5 until you add the following function;

Private Function Replace(ByVal convertString As String, ByVal swapThis As String, Optional ByVal withThis As String) As String
  ' Swaps 'swapThis' with 'withThis' in 'convertString'.
  Replace = ""
  If swapThis = "" Then swapThis = "?": withThis = swapThis
  Do While (convertString <> "")
    If Left$(convertString, Len(swapThis)) = swapThis Then
      Replace = Replace + withThis
      convertString = Mid$(convertString, Len(swapThis) + 1)
    Else
      ' Old slow code.
      ' swapString = swapString + Left$(convertString, 1)
      ' convertString = Mid$(convertString, 2)
      ' New faster code.
      Replace = Replace + Left$(convertString, InStr(convertString + swapThis, swapThis) - 1)
      convertString = Mid$(convertString, InStr(convertString + swapThis, swapThis))
    End If
  Loop
End Function

startpos = InStr(1, exp, "-") instead of startpos = InStr(1, exp, "+") after the subtract section to make it work

The article starter has earned a lot of community kudos, and such articles offer a bounty for quality replies.