' FB 1.05.0 Win64

Function ReverseString(s As Const String) As String
  If s = "" Then Return s
  Dim length As Integer = Len(s)
  Dim r As String = Space(length)
  For i As Integer = 0 To length - 1
     r[i] = s[length - 1 - i]
  Next
  Return r
End Function

Dim s As String = "asdf"
Print "'"; s; "' reversed is '"; ReverseString(s); "'"