#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
int main(int argc, char *argv[])
{
const int MASTER = 0;
const int TAG_GENERAL = 1;
int numTasks;
int rank;
int source;
int dest;
int rc;
int count;
int dataWaitingFlag;
char inMsg;
char outMsg;
MPI_Status Stat;

MPI_Init(&argc,&argv);
// Gets number of tasks/processes that this program is running on
MPI_Comm_size(MPI_COMM_WORLD, &numTasks);
// Gets the rank (process/task number) that this program is running on
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
// If the master node
if (rank == MASTER) {
// Send out messages to all the sub‐processes
for (dest = 1; dest < numTasks; dest++) {
outMsg = rand() % 256; // Generate random message to send to slave nodes
// Send a message to the destination
rc = MPI_Send(&outMsg, 1, MPI_CHAR, dest, TAG_GENERAL, MPI_COMM_WORLD);
printf("Task %d: Sent message %d to task %d with tag %d\n",
rank, outMsg, dest, TAG_GENERAL);
}
}
// Else a slave node
else {
// Wait until a message is there to be received
do {
MPI_Iprobe(MASTER, 1, MPI_COMM_WORLD, &dataWaitingFlag, MPI_STATUS_IGNORE);
printf("Waiting\n");
} while (!dataWaitingFlag);
// Get the message and put it in 'inMsg'
rc = MPI_Recv(&inMsg, 1, MPI_CHAR, MASTER, TAG_GENERAL, MPI_COMM_WORLD, &Stat);
// Get how big the message is and put it in 'count'
rc = MPI_Get_count(&Stat, MPI_CHAR, &count);
printf("Task %d: Received %d char(s) (%d) from task %d with tag %d \n",
rank, count, inMsg, Stat.MPI_SOURCE, Stat.MPI_TAG);
}
MPI_Finalize();
}