modmajorparsing.vb

visual basic课程设计案例精编

Module modMajorParsing
    Public Function GetE() As Object
        On Error GoTo ErrorHandler

        '**********************************
        '* PARSING ROUTINE (Expression E) *
        '* E ::= T + T | T - T | T        *
        '**********************************

        'Get the lower value (T)
        Value = GetT()

        'Exit function if error or help call returned


        'User set a value to a variable
        If SetVariable Then
            GetE = Value
            Exit Function
        End If

        'Allow for multiple operators of the same precedence
        'level occuring immediately after each other
        While OutputString = "+" Or OutputString = "-"

            Select Case OutputString

                'Addition operator
            Case "+"
                    ExtractToken()
                    Value = Value + GetT()

                    'Subraction operator
                Case "-"
                    ExtractToken()
                    Value = Value - GetT()

            End Select

        End While

        'Return value for E
        GetE = Value

        'Exit function before error handler
        Exit Function

ErrorHandler:

        'Trap errors
        TrapErrors(Err.Number)

    End Function

    Public Function GetT() As Object
        On Error GoTo ErrorHandler
        Dim Exponent As Double

        '****************************
        '* PARSING ROUTINE (Term T) *
        '* T ::= F * F | F / F | F  *
        '****************************

        'Get the lower value (F)
        Value = GetF()

        'Exit function if error or help call returned

        'User set a value to a variable
        If SetVariable Then
            GetT = Value
            Exit Function
        End If

        'Allow for multiple operators of the same precedence
        'level occuring immediately after each other
        While OutputString = "*" Or OutputString = "/"

            Select Case OutputString

                'Multiplication operator
            Case "*"
                    ExtractToken()
                    Value = Value * GetF()

                    'Division operator
                Case "/"
                    ExtractToken()
                    Value = Value / GetF()

            End Select

        End While
        'Return value for T
        GetT = Value
        'Exit function before error handler
        Exit Function
ErrorHandler:

        'Trap errors
        TrapErrors(Err.Number)

    End Function

    Public Function GetF() As Object
        On Error GoTo ErrorHandler
        Dim ArrayIndex As Integer
        Dim ArrayItemExists As Boolean
        Dim ArrayString As String
        Dim ArrayValue As Double
        Dim Base As Double
        Dim Constant As Double
        Dim ConstantExists As Boolean
        Dim FileNumber As Integer
        'Dim LogBase As String
        Dim LogIndex As Integer
        Dim i As Integer
        Dim Temp As String
        Dim Temp2 As String

        '******************************
        '* PARSING ROUTINE (Factor F) *
        '* F ::= Number | ( E )       *
        '******************************

        'Handle the low level calculations
        Select Case OutputString

            '***************
            'Basic Functions
            '***************

            'Number
        Case "Number"
                Value = OutputValue
                ExtractToken()
                GetF = PostToken()

                'Negative
            Case "-"
                ExtractToken()
                GetF = -(GetF())
                'Random number
            Case "rnd"
                Randomize()
                Value = Rnd()
                ExtractToken()
                GetF = PostToken()
                'Parenthesis
            Case "("
                ExtractToken()
                Value = GetE()
                If OutputString <> ")" And OutputString <> "EOS" Then
                    TrapErrors(0)
                    Exit Function
                End If
                If OutputString = "EOS" Then
                    GetF = Value
                Else
                    ExtractToken()
                    GetF = PostToken()
                End If

                'Previous answer
            Case "ans"
                Value = PrevAnswer
                ExtractToken()
                GetF = PostToken()

                '*************
                'Miscellaneous
                '*************

                'Absolute value
            Case "abs"
                ExtractToken()
                Value = GetF()
                If InError Then
                    Exit Function
                Else
                    GetF = System.Math.Abs(Value)
                End If
                'Help
            Case "sr"
                ExtractToken()
                Value = GetF()
                If InError Then
                    Exit Function
                Else
                    GetF = System.Math.Sqrt(Value)
                End If

                '**********
                'Logarithms
                '**********

                'Logarithm (to a base)
            Case "log"
                'Get logarithm base
                Base = Val(logbase)
                'Get number
                ExtractToken()
                GetF = System.Math.Log(GetF()) / System.Math.Log(Base)

                'Natural logarithm
            Case "ln"
                ExtractToken()
                Value = GetF()
                If InError Then
                    Exit Function
                Else
                    GetF = System.Math.Log(Value)
                End If
                '***********************
                'Trigonometric Functions
                '***********************

                'Cosine
            Case "cos"
                ExtractToken()
                Value = GetF()
                ConvertToRadians()
                If InError Then
                    Exit Function
                Else
                    GetF = System.Math.Cos(Value)
                End If

                'Cotangent
            Case "cot"
                ExtractToken()
                ConvertToRadians()
                If InError Then
                    Exit Function
                Else
                    GetF = 1 / System.Math.Tan(Value)
                End If
                'Cosecant
            Case "csc"
                ExtractToken()
                Value = GetF()
                ConvertToRadians()
                If InError Then
                    Exit Function
                Else
                    GetF = 1 / System.Math.Sin(Value)
                End If

                'Hyperbolic cosecant
            Case "hcsc"
                ExtractToken()
                Value = GetF()
                ConvertToRadians()
                If InError Then
                    Exit Function
                Else
                    GetF = 2 / (System.Math.Exp(Value) - System.Math.Exp(-Value))
                End If