0->1,1->2,2->3,,,n->0。循环发送

#include<stdio.h>
#include"mpi.h"
int main(int argc, char **argv)
{
    MPI_Comm comm = MPI_COMM_WORLD;
    int size, rank, latt,num = 6;
    MPI_Status status;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(comm,&size);
    MPI_Comm_rank(comm,&rank);
    latt = (rank + 1)%size;
    if(rank == 0)
    {
        MPI_Send(&num,1,MPI_INT,1,99,comm);
        printf("Process 0 send num to process 1.\n");
        MPI_Recv(&num,1,MPI_INT,size - 1,99,comm,&status);
        printf("Process 0 recv num from process %d.\n",size-1);
    }
    else {
        MPI_Recv(&num,1,MPI_INT,rank - 1,99,comm,&status);
        printf("Process %d recv num from process %d.\n",rank,rank-1);
        MPI_Send(&num,1,MPI_INT,latt,99,comm);
        printf("Process %d send num to process %d.\n",rank ,latt);
    }
    MPI_Finalize();
    return 0;
}

MPI_Comm_size(comm,&size);
MPI_Comm_rank(comm,&rank);
latt = (rank + 1)%size;