!-----  Ex8_1: 簡単なサブルーチンの例   -----
   PROGRAM main
      INTEGER :: i,j,k
      READ*, i,j,k
        IF(i<j) CALL swap(i,j)
        IF(j<k) CALL swap(j,k)
        IF(i<j) CALL swap(i,j)
      PRINT *, i,j,k
   END
! --- Swapping ---
   SUBROUTINE swap(p, q)
      INTEGER, INTENT(INOUT) :: p,q
      INTEGER :: r
      r=p;  p=q;  q=r
   END SUBROUTINE