The program first calls function TrimmedNumber to remove leading spaces, possibly on both sides of of a + or - sign.

' Remove leading spaces, possibly on both sides of
' a "-" or "+" sign. Examples:
'       "  - 12 2"      -->     "-12 2"
'       " X 12"         -->     "X12"
Private Function TrimmedNumber(ByVal txt As String) As _
    String
Dim trimmed_txt As String
Dim i As Integer
Dim ch As String

    txt = Trim$(txt)
    For i = 1 To Len(txt)
        ch = Mid$(txt, i, 1)
        If ch = " " Then
            ' Skip this space.
        ElseIf (ch >= "0") And (ch >= "0") Then
            ' This is the first digit.
            ' Copy the rest of the text.
            trimmed_txt = trimmed_txt & Mid$(txt, i)
            Exit For
        Else
            ' This is something else. Possibly a "-"
            ' or a "+", or garbage. Keep it.
            trimmed_txt = trimmed_txt & ch
        End If
    Next i

    TrimmedNumber = trimmed_txt
End Function

' Return True if the value is a valid Byte string
' (decimal not hex).
Public Function IsAByte(ByVal txt As String) As Boolean
Dim test_byte As Byte

    On Error Resume Next
    txt = TrimmedNumber(txt)
    test_byte = CByte(txt)

    If Err <> 0 Then
        IsAByte = False
    Else
        IsAByte = (CStr(test_byte) = txt)
    End If
End Function

' Return True if the value is a valid Integer string.
Public Function IsAnInteger(ByVal txt As String) As Boolean
Dim test_integer As Integer

    On Error Resume Next
    txt = TrimmedNumber(txt)
    test_integer = CInt(txt)

    If Err <> 0 Then
        IsAnInteger = False
    Else
        IsAnInteger = (CStr(test_integer) = txt)
    End If
End Function

' Return True if the value is a valid Long string.
Public Function IsALong(ByVal txt As String) As Boolean
Dim test_long As Long

    On Error Resume Next
    txt = TrimmedNumber(txt)
    test_long = CLng(txt)

    If Err <> 0 Then
        IsALong = False
    Else
        IsALong = (CStr(test_long) = txt)
    End If
End Function