1. #include <stdio.h>
2. #include <string.h>
3. #include <unistd.h>
4. #include <mpi.h>
5.  
6. int main(int argc, char **argv)
7. {
8.         int myrank;
9.         int comm_size;
10.         int message;
11.         int number;
12.         MPI_Status status;
13.         MPI_Init(&argc, &argv);
14.         sleep(5);
15.         MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
16.         MPI_Comm_size(MPI_COMM_WORLD, &comm_size);
17.  
18.         int cs = comm_size-1;
19.  
20.         if(myrank==0)
21.         {
22.                 number = 27;
23.                 printf("Process %d: Sending number %d to process %d.\n", myrank, number, (myrank+1)%comm_size);
24.                 MPI_Send(&number, 1, MPI_INT, (myrank+1)%comm_size, 0, MPI_COMM_WORLD);
25.                 printf("Process %d: Number %d sent to process %d. Awaiting number from process %d.\n", myrank, number, (myrank+1)%comm_size, cs);
26.                 MPI_Recv(&number, 1, MPI_INT, cs, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
27.                 printf("Process %d: Number %d received from process %d. Finalizing...\n", myrank, number, cs);
28.         }
29.         else
30.         {
31.                 int next = (myrank+1)%comm_size;
32.                 printf("Process %d: Awaiting a number from process %d.\n", myrank, myrank-1);
33.                 MPI_Recv(&number, 1, MPI_INT, myrank-1, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
34.  
35.                 printf("Process %d: Number %d received from process %d. Adding %d to it...\n", myrank, number, myrank-1, 10-myrank);
36.                 number = number + (10-myrank);
37.  
38.                 printf("Process %d: Resulting number: %d. Sending to process %d.\n", myrank, number, next);
39.                 MPI_Send(&number, 1, MPI_INT, next, 0, MPI_COMM_WORLD);
40.                 printf("Process %d: Number sent to process %d.\n", myrank, next);
41.  
42.         }
43.         MPI_Finalize();
44.         return 0;
45. }
46.