[RESOLVED] Array out of range.

Hi I am trying to make some code to collect tokens of a string. but I keep getting an out of range error, tho it works with some expressions
here my code.

Code:

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Public Class Form1

    Private Enum Tokypes
        None = 0
        Digit = 1
        Sysmbol = 2
    End Enum

    'Private Expression As String = "8 * 2 + (10+5)" 'Works fine on this expression.
    Private Expression As String = "8 * 2 + 1" ' VB Crys on this one why

    Private Pos As Integer = 0
    Dim sToken As String = vbNullString
    Dim sTokType As Tokypes

    Private Function isDelim(ByVal c As Char) As Boolean
        If (("+-/*%^=()".IndexOf(c) <> -1)) Then
            Return True
        End If
        Return False
    End Function

    Private Sub GetTokens()
        sToken = vbNullString
        sTokType = Tokypes.None

        If (Pos = Expression.Length) Then
            sToken = vbNullString
            sTokType = Tokypes.None
            Return
        End If

        'Skip white
        While (Pos < Expression.Length) And Char.IsWhiteSpace(Expression(Pos))
            Pos += 1
        End While
        '
        If isDelim(Expression(Pos)) Then
            sToken = sToken & Expression(Pos)
            Pos += 1
            'Token Type.
            sTokType = Tokypes.Sysmbol
        ElseIf Char.IsDigit(Expression(Pos)) Then
            'Thowing error here - Index was outside the bounds of the array.
            While Char.IsDigit((Expression(Pos)))
                sToken = sToken & Expression(Pos)
                Pos += 1
            End While
            If Pos = Expression.Length Then Return
            'Token Type.
            sTokType = Tokypes.Digit
        End If

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        GetTokens()

        While sTokType <> Tokypes.None
            MsgBox(sToken)
            GetTokens()
        End While

    End Sub
End Class

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If you run the code with this expression eveything is fine "8 * 2 + (10+5)"
But if you run it with this you get an out of range error. 8 * 2 + 1
I don't see why cos the first expression has more length than the second.

your problem occurs in the code below when you enter the loop and Pos = 8. When Pos is 8,Char.IsDigit is true because Expression(8)="1". In the loop you then increment Pos, loop and look at Expression(9) which doesn't exist because the upper index of the string array is 8.

You need to change your code to test Pos and jump out of the While or rearrange your logic.

Code:

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While Char.IsDigit((Expression(Pos)))
                sToken = sToken & Expression(Pos)
                Pos += 1
            End While

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kevin

Thanks

Think I fixed it I appened an extra white space to the end of the expression and it seems to work. I left the code here in case someone else may need it, updated for Alpha.

Code:

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Public Class Form1

    Private Enum Tokypes
        None = 0
        Digit = 1
        Alpha = 2
        Sysmbol = 3
    End Enum

    Private Expression As String = "PI+8 * 2 + 500 *9 * SIN(3)"

    Private Pos As Integer = 0
    Dim sToken As String = vbNullString
    Dim sTokType As Tokypes

    Private Function isDelim(ByVal c As Char) As Boolean
        If ((" +-/*%^=()".IndexOf(c) <> -1)) Then
            Return True
        End If
        Return False
    End Function

    Private Sub GetTokens()
        sToken = vbNullString
        sTokType = Tokypes.None

        While Pos < Expression.Length AndAlso Char.IsWhiteSpace(Expression(Pos))
            Pos += 1
        End While

        If (Pos = Expression.Length) Then
            sToken = vbNullString
            sTokType = Tokypes.None
            Return
        End If

        If isDelim(Expression(Pos)) Then
            sToken = Expression(Pos)
            Pos += 1
            'Token Type.
            sTokType = Tokypes.Sysmbol
        ElseIf Char.IsLetter(Expression(Pos)) Then
            While Not isDelim(Expression(Pos))
                sToken = sToken & Expression(Pos)
                Pos += 1
                If (Pos >= Expression.Length) Then
                    Return
                End If
            End While
            'Token Type.
            sTokType = Tokypes.Alpha
        ElseIf Char.IsDigit(Expression(Pos)) Then
            While Not isDelim(Expression(Pos))
                sToken = sToken & Expression(Pos)
                Pos += 1
                If (Pos >= Expression.Length) Then
                    Return
                End If
            End While
            'Token Type.
            sTokType = Tokypes.Digit
        Else

        End If

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Pos = 0
        GetTokens()

        While sTokType <> Tokypes.None
            MsgBox(sToken)
            GetTokens()
        End While

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Expression = Expression & " "
    End Sub
End Class

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What is this code supposed to accomplish?

Quote:

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Originally Posted by dbasnett

What is this code supposed to accomplish?

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tokenizer for a math evaluator I am going to make.

I thought so. This may be useful Parsing Infix