PROGRAM vaihtotesti
  IMPLICIT NONE
  REAL :: x = 1.0, y = -1.0
  WRITE (*,*) 'x,y: ', x, y
  IF (x > y) THEN
    CALL vaihda(x,y)
  END IF
  WRITE (*,*) 'x,y: ', x, y
CONTAINS
  SUBROUTINE vaihda(a,b)
    IMPLICIT NONE
    REAL :: a, b
    REAL :: apu
    apu = a
    a = b
    b = apu
  END SUBROUTINE vaihda
END PROGRAM vaihtotesti