ARGH! Equation solver program

[alkatran]

To start, it doesn't actually solve equations yet. It only sums them up.. erm...

It changes 4+5*6^2 to 1300

ANYWAYS. I have run into problems. Here's the (large amount of) code:

Public Function SolveEquation(ByVal Equation As String)
Dim A As Long
Dim B As Long
Dim C As Long
Dim LastBracket As Long
Dim Level As Long
Dim BracketLevel As Long
Dim Number As Single
 
    'Go through equation, adding parantheses for PEDMAS
    Level = 1
    Do While A <= Len(Equation)
        A = A + 1
        Select Case Mid(Equation, A, 1)
        Case "("
            BracketLevel = BracketLevel + 1
        Case ")"
            BracketLevel = BracketLevel - 1
        Case "+", "-"
            Select Case Level
            Case 2, 3
                Equation = Left(Equation, A - 1) & ")" & Mid(Equation, A, Len(Equation))
                BracketLevel = BracketLevel - 1
            End Select
            Level = 1
        Case "/", "\", "*"
            Select Case Level
            Case 1
                'Open parenthese before number
                For B = A - 1 To 1 Step -1
                    Select Case Mid(Equation, B, 1)
                    Case "+", "-"
                        Equation = Left(Equation, B) & "(" & Mid(Equation, B + 1, Len(Equation))
                        BracketLevel = BracketLevel + 1
                        B = 0
                    End Select
                    If B = 1 Then
                        Equation = "(" & Equation
                        BracketLevel = BracketLevel + 1
                        B = 0
                    End If
                Next B
            Case 3
                Equation = Left(Equation, A - 1) & ")" & Mid(Equation, A, Len(Equation))
                BracketLevel = BracketLevel - 1
            End Select
            Level = 2
        Case "^"
            Select Case Level
            Case 1, 2
                'Open parenthese before number
                For B = A - 1 To 1 Step -1
                    Select Case Mid(Equation, B, 1)
                    Case "+", "-", "*", "/", "\"
                        Equation = Left(Equation, B) & "(" & Mid(Equation, B + 1, Len(Equation))
                        BracketLevel = BracketLevel + 1
                        B = 0
                    End Select
                    If B = 1 Then
                        Equation = "(" & Equation
                        BracketLevel = BracketLevel + 1
                        B = 0
                    End If
                Next B
            End Select
            Level = 3
        Case " "
        Case Else 'number
        End Select
    Loop
    For BracketLevel = BracketLevel To 1 Step -1
        Equation = Equation & ")"
    Next BracketLevel
    Equation = "(" & Equation & ")"
    'Equation prepped
    
    'Begin solving
    A = 0
    Level = 0
    'Logic: Loop throug equation, looking for ")" and storing "("
    'Solve from last "(" to ")", since it is all on same level
    'Start from beginning of equation with solved bracket
    'Repeat until no brackets left
    
    'Loop through equation
    Do While A <= Len(Equation)
        A = A + 1
        Select Case Mid(Equation, A, 1)
        Case "("
            LastBracket = A
        Case ")"
            'Since brackets are being closed, this is
            'the highest in PEDMAS, solve inside brackets
            B = LastBracket
            'using bracket level as a true/false
            BracketLevel = 0
            Do Until BracketLevel
                B = B + 1
                Select Case Mid(Equation, B, 1)
                Case "+"
                    Level = 1
                Case "-"
                    Level = 2
                Case "\", "/"
                    Level = 3
                Case "*"
                    Level = 4
                Case "^"
                    Level = 5
                Case ")"
                    A = B
                    BracketLevel = 1 'exit the loop, bracket solved
                    'remove brackets and leave solved number
                    Equation = Left(Equation, LastBracket - 1) & CStr(Number) & Mid(Equation, A, Len(Equation))
                Case Else
                    C = 0
                    'Get the entire number, not just 1st digit
                    Do While IsNumeric(Mid(Equation, C + B, 1)) Or Mid(Equation, C + B, 1) = "."
                        C = C + 1
                    Loop
                    'If this isn't the first number (>4< + 5), (1st + 2nd)
                    If Level Then
                        Select Case Level
                        Case 1 'Addition
                            Number = Number + CSng(Mid(Equation, B, C))
                        Case 2 'Subtraction
                            Number = Number - CSng(Mid(Equation, B, C))
                        Case 3 'Division
                            If CSng(Mid(Equation, B, C)) = 0 Then
                                Number = 0
                            Else
                                Number = Number / CSng(Mid(Equation, B, C))
                            End If
                        Case 4 'Multiplication
                            Number = Number * CSng(Mid(Equation, B, C))
                        Case 5 'Exponential
                            Number = Number ^ CSng(Mid(Equation, B, C))
                        End Select
                        Number = CSng(Format(Number, "########0.####"))
                        Equation = Left(Equation, LastBracket) & CStr(Number) & Mid(Equation, B + C, Len(Equation))
                        B = LastBracket
                        Level = 0
                    Else
                        Number = CSng(Mid(Equation, B, C))
                        B = B + C - 1 'Put B at the end of the number
                    End If
                End Select
            Loop
            'get rid of brackets
            Equation = Left(Equation, B - 2) & Mid(Equation, B, Len(Equation))
            'Start solving from start again, with brackets solved
            A = 0
            Level = 0
            LastBracket = 0
        End Select
        'Wouldn't want a nasty inescapable infinite loop
        DoEvents
    Loop
    SolveEquation = Equation
End Function

The problem is usually right after the format(...) near the end. It says type mismatch... grrr...


Anyways, it's great if you see the problem. If you have any pointers, shout them out. I'll be toiling on this.

*edit* commented code a bit

[jemidiah]

For me, it works fine as long as you don't give it a variable. Is that the problem or did I miss something?

[alkatran]

What do you mean don't give it a variable? (don't tell me I;ve been calling it wrong! )

[jemidiah]

If I pass it a normal mathmatical operation (say... (1+2)^5) it works fine. With, say, (1+a)^5=6, it gives the error.

PS. I haven't actually looked at the code; I'm lazy and want to know what to look for first

[alkatran]

It doesn't actually solve equations, it just simplifies them to a single number... the name is sortof misleading, lol.

[Acidic]

hehe, this can be done in a few lines of HTML:

<html>
<input type="text" onBlur="this.value=eval(this.value)">
</html>

if you type in 3+4, it will return 7.

you can also use it to store variables.

eg.
a=Math.pi

then 2*a will return 6.2...

[alkatran]

That is awsome Acidic. But it destroys the point!

[Acidic]

Originally posted by alkatran
That is awsome Acidic. But it destroys the point!

thx and sorry.

[jemidiah]

Well, you can actually add a reference to the MS Script control and use its Eval function in much the same way from VB, though I thought you wanted to write your own parser