! The Towers Of Hanoi
! FORTRAN 90
! Copyright (C) 2002 Amit Singh. All Rights Reserved.
! http://hanoi.kernelthread.com
!
! Tested under Intel Fortran Compiler 6.0 for Linux
! Compile as follows:
!
!   $IFC_ROOT/compiler60/ia32/bin/ifc hanoi.f -o hanoi -lPEPCF90
!
        PROGRAM MAIN
                 INTEGER :: argc
                 INTEGER :: N
                 CHARACTER*128 BUFFER
                 argc = IARGC()
                 IF (argc /= 1) THEN
                     PRINT *, 'usage: hanoi <n>'
                     CALL EXIT()
                 END IF
                 CALL GETARG(1, BUFFER)
                 READ(BUFFER, *) N
                 IF (N < 1) THEN
                     PRINT *, 'usage: hanoi <n> (<n> is a +-ve integer)'
                     CALL EXIT()
                 END IF
                 CALL HANOI(N)
        END PROGRAM MAIN

        FUNCTION HANOI(n) RESULT (dummy)
            INTEGER :: dummy
            CALL XHANOI(n, 1, 2, 3)
            dummy = 1
        END FUNCTION HANOI

        FUNCTION MOVEDISK(from, to) RESULT (dummy)
            INTEGER :: dummy
            INTEGER, INTENT (IN) :: from, to
            PRINT *, from, ' --> ', to
            dummy = 1
        END FUNCTION MOVEDISK

        RECURSIVE FUNCTION XHANOI(n, from, using, to) RESULT (dummy)
            INTEGER :: dummy
            INTEGER, INTENT (IN) :: n, from, using, to
            IF (n < 1) THEN
                dummy = 1
            ELSE
                dummy = XHANOI(n-1, from, to, using)
                dummy = MOVEDISK(from, to)
                dummy = XHANOI(n-1, using, from, to)
            END IF
        END FUNCTION XHANOI