VB表达式计算函数

今天自己写的一个函数，没想到会用了将近两个小时……
还没有进行优化，估计这个函数的效率不怎么样。
没有错误检查功能。如果表达式有问题，那么结果是不可预知的。
写完后调试了半天，检查出多处错误。
如果发现还存在问题请告诉我。

感谢声明：感谢Aegisys[0GiNr]发现未检查减法运算的错误

'函数：Calc(Exp As String) As Double
'用于计算包含括号、四则运算的字符串表达式

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Public Function Calc(Exp As String) As Double
    '去空格
    Exp = Replace(Exp, " ", "")
    '去掉最外括号
    While Left(Exp, 1) = "(" And Right(Exp, 1) = ")"
        Exp = Mid(Exp, 2, Len(Exp) - 2)
    Wend
    Calc = CalcA(Exp)
End Function

Public Function CalcA(Exp As String) As Double
    'Deep = Deep + 1
    '(1+2)*3+4*5+2=?
    '(1+2)*(3+4)+5=?
    '(1+2)*((3+4)*5)+3=?
    '11111012222211100
    
    DoEvents '防止死机
    Dim LvS As Integer
    
    '循环变量
    Dim I As Integer, J As Integer
    
    '对于纯数值
    If Trim(Str(Val(Exp))) = Trim(Exp) Then
        CalcA = Val(Exp)
        GoTo LAB_END
    ElseIf Exp = "" Then '对于空（负号）
        CalcA = 0
        GoTo LAB_END
    End If

    'Dim AscN As Integer
    'For I = 1 To Len(Exp)
    '    AscN = Asc(Mid(Exp, I, 1))
    '    If AscN > 57 Or AscN < 43 Or AscN = 47 Or AscN = 44 Then GoTo LAB_NUM
    'Next
    'CalcA = Val(Exp)
    'GoTo LAB_END
'LAB_NUM:
        
    '括号跳转
    For I = 1 To Len(Exp)
        If Mid(Exp, I, 1) = "(" Then
            LvS = I
            GoTo LAB_A1
        End If
    Next
    GoTo LAB_A2
    
LAB_A1:
    '对于有括号的表达式
        '存储级别（优化备用）
        'Dim Lv() As Integer
        'ReDim Lv(Len(Exp)) As Integer
        '当前级别，最大级别，最大级别启始，结束，判定
        Dim CurrentLv As Integer, LvM As Integer, LvMS As Integer, LvME As Integer, LvMB As Boolean
        
        CurrentLv = 0: LvMB = False
        '定级
        For I = LvS To Len(Exp)
            If Mid(Exp, I, 1) = "(" Then
                CurrentLv = CurrentLv + 1
                If CurrentLv > LvM Then
                    LvM = CurrentLv
                    LvMS = I '最大级别启始点
                    LvMB = True
                End If
            ElseIf Mid(Exp, I, 1) = ")" Then
                CurrentLv = CurrentLv - 1
                If LvMB Then
                    LvME = I '最大级别结束点
                    LvMB = False
                End If
            End If
            'Lv(I) = CurrentLv '存储级别（优化备用）
        Next
        '计算最高级括号
        Exp = Left(Exp, LvMS - 1) & CalcA(Mid(Exp, LvMS + 1, LvME - LvMS - 1)) & Right(Exp, Len(Exp) - LvME)
        CalcA = CalcA(Exp)
        GoTo LAB_END

LAB_A2:
    '对于没有括号的表达式
        '加减法跳转
        Dim AscS As Integer
        For I = 1 To Len(Exp)
            If Mid(Exp, I, 1) = "+" Then GoTo LAB_B1
            If Mid(Exp, I, 1) = "-" And I > 1 Then
                AscS = Asc(Mid(Exp, I - 1, 1))
                If AscS >= Asc("0") And AscS < Asc("9") Then GoTo LAB_B1
            End If
        Next
        GoTo LAB_B2
LAB_B1:
        '对于有加减法的表达式
            For I = 1 To Len(Exp)
                '计算加减法
                If Mid(Exp, I, 1) = "+" Then
                    Exp = CalcA(Left(Exp, I - 1)) + CalcA(Right(Exp, Len(Exp) - I))
                    CalcA = CalcA(Exp)
                    GoTo LAB_END
                ElseIf Mid(Exp, I, 1) = "-" Then
                    Exp = Str(CalcA(Left(Exp, I - 1)) - CalcA(Right(Exp, Len(Exp) - I)))
                    CalcA = CalcA(Exp)
                    GoTo LAB_END
                End If
            Next
LAB_B2:
        '对于没有加减法的表达式
            For I = 1 To Len(Exp)
                '计算乘除法
                If Mid(Exp, I, 1) = "*" Then
                    Exp = Str(CalcA(Left(Exp, I - 1)) * CalcA(Right(Exp, Len(Exp) - I)))
                    CalcA = CalcA(Exp)
                    GoTo LAB_END
                ElseIf Mid(Exp, I, 1) = "/" Then
                    Exp = Str(CalcA(Left(Exp, I - 1)) / CalcA(Right(Exp, Len(Exp) - I)))
                    CalcA = CalcA(Exp)
                    GoTo LAB_END
                End If
            Next
LAB_END:
    'Deep = Deep - 1
End Function