Reason for MPI 'rc' variable and MPI_Get_Count() - c

Question

In the ping-pong program below, what use is the rc variable? It is constantly updated but never used.
Plus what does MPI_Get_Count() do?
#include "mpi.h"
#include <stdio.h>
int main(int argc, char * argv [])
int numtasks, rank, dest, source, rc, count, tag=1;
char inmsg, outmsg;
MPI_Status Stat ;
MPI_Init (&argc,&argv);
MPI_Comm_size (MPI_COMM_WORLD, &numtasks);
MPI_Comm_rank (MPI_COMM_WORLD, &rank);
if (rank == 0) {
dest = source = 1;outmsg=’x’;
rc = MPI_Send (&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
rc = MPI_Recv (&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
}
else if (rank == 1) {
dest = source = 0;outmsg=’y’;
rc = MPI_Recv (&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
rc = MPI_Send (&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
}
rc = MPI_Get_count (&Stat, MPI_CHAR, &count);
printf("Task %d: Received %d char(s) from task %d with tag %d \n", rank, count, Stat.MPI_SOURCE,Stat.MPI_TAG);
MPI_Finalize ();
}

Answer 1

The bit about MPI_Get_count is answered by the documentation in the "Output" section, further down that linked page.
As for rc, here's the best explanation I can offer with no access to the author of this code or any related notes. all MPI routines in the C bindings return an error code. Some compilers check whether one is dropping return values on the floor, as it might indicate an error in the code, and generate warnings where they see that happen. Thus, to keep those warnings from appearing, this code assigns the return value to the variable rc.
That said, many compilers also warn about setting a variable that's never used, which is the case here. An idiom for telling a compiler "yes, I know I'm ignoring this return value, leave me alone" is (void)function_call(foo, bar, baz); (i.e. cast the return value to void). This is most often seen on calls to functions whose return value really should be checked, like write(). Writing it on every MPI call rather than silencing an offending warning would be rather ugly.