MPIprograms / main

#include <iostream>
#include "mpi.h"

int main( int argc, char **argv ) {
  using std::cin; using std::cout; using std::endl;
  int flag; MPI_Initialized(&flag);
  if ( !flag ) MPI_Init( &argc, &argv );
  int myrank; MPI_Comm_rank( MPI_COMM_WORLD, &myrank );
  int commsize; MPI_Comm_size( MPI_COMM_WORLD, &commsize );
  MPI_Status status;
  char source[256]; 
  char dest[256];
  if ( myrank == 0 ) {
      cout << "Process 0: what to send? "; cin >> source;
    MPI_Send( source, strlen(source)+1, MPI_CHAR, 1, 0, MPI_COMM_WORLD );
      cout << "Process 0 has sent " << source << endl;
    MPI_Recv( dest, 256, MPI_CHAR, commsize-1, 0, MPI_COMM_WORLD, &status );
      cout << "Process 0 has received " << dest << endl;
  }
  else {
    MPI_Recv( dest, 256, MPI_CHAR, myrank-1, 0, MPI_COMM_WORLD, &status );
      cout << "Process " << myrank << " has received " << dest << endl;
      itoa( myrank, source, 10 ); strcat( dest, " " ); strcat( dest, source );
    MPI_Send( dest, strlen(dest)+1, MPI_CHAR, (myrank+1) % commsize, 0, MPI_COMM_WORLD );
      cout << "Process " << myrank << " has sent " << dest << endl;
  }
  MPI_Finalize();
  return 0;
}