Write a program where two processes send and receive a message to/from
each other using MPI_Send and MPI_Recv.
The message content should be an integer array, where each element is initialised to the rank of the process. After receiving a message, each process should print out its own rank, number of elements it received, and the first element in the received array.
You may start from scratch or use exchange.cpp (or exchange.F90 for Fortran) as a starting point.
Try increasing the message size (e.g. to 100000), recompile and run. What happens? What if you reorder the send and receive calls in one of the processes?