从网下上的一个用正则表达是做的表达式计算器，它的加减法有有关问题，哪一位高手能够帮助修改正确，多谢！

 
Imports System.Text.RegularExpressions
Public Class Form2
    Public Primitives As New Hashtable
    Function Evaluate(ByVal expr As String) As Double
        Const Num As String = "(\-?\d+\.?\d*)"
        Const Func1 As String = "(exp|log|log10|abs|sqr|sqrt|sin|cos|tan|asin|acos|atan)"
        Const Func2 As String = "(atan2)"
        Const FuncN As String = "(min|max)"
        Const Constants As String = "(e|pi)"

        Dim rePower As New Regex(Num & "\s*(\^)s*" & Num)
        Dim reAddSub As New Regex(Num & "\s*([-+])s*" & Num)
        Dim reMulDiv As New Regex(Num & "\s*([*/])s*" & Num)
        Dim reFunc1 As New Regex(Func1 & "\(\s*((\((?<o>\()|(?<-o>\))|[^()]+(?(o)(?!)))+)\s*\)", RegexOptions.IgnoreCase)
        Dim reFunc2 As New Regex(Func2 & "\(\s*" & Num & "\s*,\s*" & Num & "\s*\)", RegexOptions.IgnoreCase)
        Dim reFuncN As New Regex(FuncN & "\((\s*" & Num & "\s*,)+\s*" & Num & "\s*\)", RegexOptions.IgnoreCase)
        Dim reSign1 As New Regex("([-+/*^])\s*\+")
        Dim reSign2 As New Regex("\-\s*\-")
        Dim rePar As New Regex("(?<![A-Za-z0-9])\(\s*([-+]?\d+.?\d*)\s*\)")
        Dim reNum As New Regex("^\s*[-+]?\d+\.?\d*\s*$")
        Dim reConst As New Regex("\s*" & Constants & "\s*", RegexOptions.IgnoreCase)

        expr = reConst.Replace(expr, AddressOf DoConstants)
        Do Until reNum.IsMatch(expr)
            Dim saveExpr As String = expr
            Do While rePower.IsMatch(expr)
                expr = rePower.Replace(expr, AddressOf DoPower)
            Loop
            Do While reMulDiv.IsMatch(expr)
                expr = reMulDiv.Replace(expr, AddressOf DoMulDiv)
            Loop
            Do While reFuncN.IsMatch(expr)
                expr = reFuncN.Replace(expr, AddressOf DoFuncN)
            Loop
            Do While reFunc2.IsMatch(expr)
                expr = reFunc2.Replace(expr, AddressOf DoFunc2)
            Loop
            Do While reFunc1.IsMatch(expr)
                expr = reFunc1.Replace(expr, AddressOf DoFunc1)
            Loop
            expr = reSign1.Replace(expr, "$1")
            expr = reSign2.Replace(expr, "+")
            Do While reAddSub.IsMatch(expr)
                expr = reAddSub.Replace(expr, AddressOf DoAddsub)
            Loop
            expr = rePar.Replace(expr, "$1")
        Loop
        Return CDbl(expr)
    End Function
    Function DoConstants(ByVal m As Match) As String
        Select Case m.Groups(1).Value.ToUpper
            Case "PI"
                Return Math.PI.ToString
            Case "E"
                Return Math.E.ToString
            Case Else
                Return vbNullString
        End Select
    End Function
    Function DoPower(ByVal m As Match) As String
        Dim n1 As Double = CDbl(m.Groups(1).Value)
        Dim n2 As Double = CDbl(m.Groups(3).Value)
        Return (n1 ^ n2).ToString
    End Function
    Function DoMulDiv(ByVal m As Match) As String
        Dim n1 As Double = CDbl(m.Groups(1).Value)
        Dim n2 As Double = CDbl(m.Groups(3).Value)
        Select Case m.Groups(2).Value
            Case "/"
                Return (n1 / n2).ToString
            Case "*"
                Return (n1 * n2).ToString
            Case Else
                Return vbNullString
        End Select
    End Function
    Function DoAddsub(ByVal m As Match) As String

        Dim n1 As Single = CDec(m.Groups(1).Value)
        Dim n2 As Single = CDec(m.Groups(3).Value)
        Select Case m.Groups(2).Value
            Case "+"
                Return (n1 + n2).ToString
            Case "-"
                Return (n1 - n2).ToString
            Case Else
                Return vbNullString
        End Select
    End Function
    Function DoFunc1(ByVal m As Match) As String
        Dim n1 As String = m.Groups(2).Value
        Select Case m.Groups(1).Value.ToUpper
            Case "EXP"
                Return Math.Exp(n1).ToString
            Case "LOG"
                Return Math.Log(n1).ToString
            Case "LOG10"
                Return Math.Log10(n1).ToString
            Case "ABS"
                Return Math.Abs(CDec(n1)).ToString
            Case "SQR", "SQRT"
                Return Math.Sqrt(n1).ToString
            Case "SIN"
                Return Math.Sin(n1).ToString
            Case "COS"
                Return Math.Cos(n1).ToString
            Case "TAN"
                Return Math.Tan(n1).ToString
            Case "ASIN"
                Return Math.Asin(n1).ToString
            Case "ACOS"
                Return Math.Acos(n1).ToString
            Case "ATAN"
                Return Math.Atan(n1).ToString
            Case Else
                Return vbNullString
        End Select

    End Function
    Function DoFunc2(ByVal m As Match) As String
        Dim n1 As Double = CDbl(m.Groups(2).Value)
        Dim n2 As Double = CDbl(m.Groups(3).Value)
        Select Case m.Groups(1).Value.ToUpper
            Case "ATAN2"
                Return Math.Atan2(n1, n2).ToString
            Case Else
                Return vbNullString
        End Select
    End Function
    Function DoFuncN(ByVal m As Match) As String
        Dim args As New ArrayList()
        Dim i As Integer = 2
        Do While m.Groups(i).Value <> ""
            args.Add(CDbl(m.Groups(i).Value.Replace(","c, " "c)))
            i += 1
        Loop
        Select Case m.Groups(1).Value.ToUpper
            Case "MIN"
                args.Sort()
                Return args(0).ToString
            Case "MAX"
                args.Sort()
                Return args(args.Count - 1).ToString
            Case Else
                Return vbNullString
        End Select
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox2.Text = Evaluate(TextBox1.Text)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub


End Class