' FB 1.05.0 Win64

Dim Shared symbols(0 To 15) As UByte
For i As Integer = 48 to 57
  symbols(i - 48) = i
Next
For i As Integer = 97 to 102
  symbols(i - 87) = i
Next

Const plus  As UByte = 43
Const minus As Ubyte = 45
Const dot   As UByte = 46

Function isNumeric(s As Const String, base_ As Integer = 10) As Boolean
  If s = "" OrElse s = "."  OrElse s = "+" OrElse s = "-" Then Return False
  Err = 0

  If base_ < 2 OrElse base_ > 16 Then
    Err = 1000
    Return False
  End If

  Dim t As String = LCase(s)

  If (t[0] = plus) OrElse (t[0] = minus) Then
     t = Mid(t, 2)
  End If

  If Left(t, 2) = "&h" Then
    If base_ <> 16 Then Return False
    t = Mid(t, 3)
  End if

  If Left(t, 2) = "&o" Then
    If base_ <> 8 Then Return False
    t = Mid(t, 3)
  End if

  If Left(t, 2) = "&b" Then
    If base_ <> 2 Then Return False
    t = Mid(t, 3)
  End if

  If Len(t) = 0 Then Return False
  Dim As Boolean isValid, hasDot = false

  For i As Integer = 0 To Len(t) - 1
    isValid = False

    For j As Integer = 0 To base_ - 1
      If t[i] = symbols(j) Then
        isValid = True
        Exit For
      End If
      If t[i] = dot Then
        If CInt(Not hasDot) AndAlso (base_ = 10) Then
          hasDot = True
          IsValid = True
          Exit For
        End If
        Return False ' either more than one dot or not base 10
      End If
    Next j

    If Not isValid Then Return False
  Next i

  Return True
End Function

Dim s As String
s = "1234.056789"
Print s, " (base 10) => "; isNumeric(s)
s = "1234.56"
Print s, " (base 7)  => "; isNumeric(s, 7)
s = "021101"
Print s, " (base 2)  => "; isNumeric(s, 2)
s = "Dog"
Print s, " (base 16) => "; isNumeric(s, 16)
s = "Bad125"
Print s, " (base 16) => "; isNumeric(s, 16)
s = "-0177"
Print s, " (base 8)  => "; isNumeric(s, 8)
s = "+123abcd.ef"
Print s, " (base 16) => "; isNumeric(s, 8)
s = "54321"
Print s, " (base 6)  => "; isNumeric(s, 6)
s = "123xyz"
Print s, " (base 10) => "; isNumeric(s)
s = "xyz"
Print s, " (base 10) => "; isNumeric(s)
Print
Print "Press any key to quit"
Sleep