program main
USE MPIUTILS
implicit none
integer rank, num_nodes
character(LEN=50) msg,num
integer length,anysource

!! start MPI
call MPISTART()

!! obtain the total number of processors
num_nodes=MPINUMNODES()

!! obtain the rank of this processor
rank=MPIRANK()

!! if you simply use print*  or write(*,*), all processors will write the same message to the standard output (screen).
!! MPIWRITE only write the message once.
call MPIWRITE("type in any words:")

!! MPIREAD read msg from the standard input (keyboard) and broadcast it to all processors.
call MPIREAD(msg)

!! all processors will print this.
print*,trim(msg)," from rank",rank


if(rank.gt.0)then
	num=""
	write(num,*)rank
	write(*,*) 'Hello World from rank #'//trim(adjustl(num))
	msg="Greeting from processor #"//trim(adjustl(num))

        !!send the msg to processor #0, with tag 0
	call MPISEND(0,0,msg)

        !! send the length of the msg to processor #0, with tag 1
	call MPISEND(0,1,LEN_TRIM(msg))

else
        
	write(*,"(a10,i2,a6)") "There are ",num_nodes," nodes"

	do rank=1,num_nodes-1

           !! recieve a msg with tag 0 (from any source)
		call MPIRECVANYSOURCE(anysource,0,msg)
           !! now the # of source who send the msg is written into the variable anysource

           !! recieve the length of msg from the same source
		call MPIRECV(anysource,1,length)

            !! write the msg to screen
		write(*,*) msg(1:length)
	enddo

endif

!! stop MPI
call MPIEND()

end program