Program optional_example
  Call one('Hello')
  Call one
Contains
  Subroutine one(x)
    Character(*), Intent(In), Optional :: x
    Print *, 'one: x is present =', Present(x)
    Call two(x)
  End Subroutine
  Subroutine two(y)
    Character(*), Intent(In), Optional :: y
    If (Present(y)) Then
      Print *, 'two: y is present with value "', y, '"'
    Else
      Print *, 'two: y is not present'
    End If
  End Subroutine
End Program