MPIprograms / main2

#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 );
  if ( myrank == 0 ) {
    MPI_Status *statuses = new MPI_Status[commsize-1];
    MPI_Request *requests = new MPI_Request[commsize-1];
    char *source = new char[commsize*256]; 
    char *dest = new char[commsize*256];
    for ( int i = 1; i < commsize; i++ ) {
      cout << "Process 0: what to send to process " << i << "? "; 
      cin >> &source[i*256];
    }
    for ( int i = 1; i < commsize; i++ )
      MPI_Isend( &source[i*256], strlen( &source[i*256] )+1, MPI_CHAR, i, 0, MPI_COMM_WORLD, &requests[i-1] );
    MPI_Waitall( commsize-1, requests, statuses ); 
      cout << "Process 0 has sent all messages\n";
    for ( int i = 1; i < commsize; i++ )
      MPI_Irecv( &dest[i*256], 256, MPI_CHAR, i, 0, MPI_COMM_WORLD, &requests[i-1] );
    MPI_Waitall( commsize-1, requests, statuses );
      cout << "Process 0 has received:\n";
    for ( int i = 1; i < commsize; i++ )
      cout << &dest[i*256] << " from process " << i << endl;
  }
  else {
    MPI_Status status;
    MPI_Request request;
    char source[256]; 
    char dest[256];
    MPI_Recv( dest, 256, MPI_CHAR, 0, 0, MPI_COMM_WORLD, &status );
      cout << "Process " << myrank << " has received " << dest << endl;
      itoa( myrank, source, 10 ); strcat( dest, " " ); strcat( dest, source );
    MPI_Isend( dest, strlen( dest )+1, MPI_CHAR, 0, 0, MPI_COMM_WORLD, &request );
      cout << "Process " << myrank << " has sent " << dest << endl;
  }
  MPI_Finalize();
  return 0;
}