by Mike Toye (5 Submissions)
Category: Math/Dates
Compatability: Visual Basic 3.0
Difficulty: Beginner
Date Added: Wed 3rd February 2021
Rating: 
(2 Votes)
evaluate basic math strings function
Inputs
math formula, eg; (6+(4.322^6)+(9*7)
Code Returns
result
Side Effects
no bad char validation!
VBcodersFunction Eval(sin As String) As Double
Dim bAreThereBrackets As Boolean
Dim x As Double, y As Double, z As Double
Dim L2R As Integer
Dim sLeft As String, sMid As String, sRight As String
Dim dStack As Double
Dim sPrevOp As String
Dim bInnerFound As Boolean
sin = IIf(InStr(sin, " ") > 0, RemoveAllSpaces(sin), sin)
If InStr(sin, "(") Then
'work from left to right. find the inner most
'brackets and resolve them into the string, eg;
'(6+7+(6/3)) becomes (6+7+2)
L2R = 1
While InStr(sin, "(") > 0
'inner loop
bInnerFound = False
Do
x = InStr(L2R, sin, "(")
y = InStr(x + 1, sin, "(")
z = InStr(x + 1, sin, ")")
If y = 0 Then
L2R = x
bInnerFound = True
Else
If y < z Then
L2R = y
Else
L2R = x
bInnerFound = True
End If
End If
Loop Until bInnerFound
x = InStr(L2R, sin, ")")
sin = Left(sin, L2R - 1) & CStr(Eval(Mid(sin, L2R + 1, x - L2R - 1))) & Mid(sin, x + 1)
Debug.Print sin
Wend
Eval = CDbl(IIf(IsNumeric(sin), sin, Eval(sin)))
Else
dStack = 0
sLeft = ""
sPrevOp = ""
For L2R = 1 To Len(sin)
If Not IsNumeric(Mid(sin, L2R, 1)) And Mid(sin, L2R, 1) <> "." Then
'we have an operator
If dStack = 0 Then
dStack = CDbl(sLeft)
Else
dStack = ASMD(dStack, sLeft, sPrevOp)
End If
sLeft = ""
sPrevOp = Mid(sin, L2R, 1)
Else
'carry on extracting the current number
sLeft = sLeft & Mid(sin, L2R, 1)
End If
Next L2R
If sLeft > "" Then
dStack = ASMD(dStack, sLeft, sPrevOp)
End If
Eval = dStack
End If
End Function
Function RemoveAllSpaces(sin As String) As String
Dim x As Integer
RemoveAllSpaces = ""
For x = 1 To Len(sin)
If Mid(sin, x, 1) <> " " Then
RemoveAllSpaces = RemoveAllSpaces & Mid(sin, x, 1)
End If
Next x
End Function
Function ASMD(dIn As Double, sin As String, sOP As String) As Double
Select Case sOP
Case "+"
ASMD = dIn + CDbl(sin)
Case "-"
ASMD = dIn - CDbl(sin)
Case "*"
ASMD = dIn * CDbl(sin)
Case "/"
ASMD = dIn / CDbl(sin)
Case "^"
ASMD = dIn ^ CDbl(sin)
Case Else
ASMD = 0
End Select
End Function
