Fatal error in MPI_Send: Invalid rank, error stack - c++

Question

I am writing code with mpi in c++, and I have done this:
#include <stdio.h>
#include "mpi.h"
#define NMAX 100
#define NTIMES 10
int main(int argc, char **argv)
{
int rank, size, i, n, lmax;
double time_start, time, bandwidth, max, a[NMAX];
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
time_start = MPI_Wtime();
n = 0;
max = 0.0;
lmax = 0;
while(n<=NMAX){
time_start = MPI_Wtime();
for(i = 0; i<NTIMES; i++){
if(rank==0){
MPI_Send(a, n, MPI_DOUBLE, 1, 0, MPI_COMM_WORLD);
MPI_Recv(a, n, MPI_DOUBLE, 1, 1, MPI_COMM_WORLD, &status);
}
if(rank==1){
MPI_Recv(a, n, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD, &status);
MPI_Send(a, n, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD);
}
}
time = (MPI_Wtime()-time_start)/(2*NTIMES);
bandwidth = (sizeof(double)*n*1.0/(1024*1024*time));
if(max<bandwidth){
max = bandwidth;
lmax = sizeof(double)*n;
}
if(rank==0)
if(n==0) printf("latency = %lf seconds\n", time);
else printf("%d bytes, bandwidth = %lf Mb/s\n", (int)sizeof(double)*n, bandwidth);
if(n==0) n = 1;
else n = 2*n;
}
if(rank==0) printf("max bandwidth = %lf Mb/s length = %d bytes\n", max, lmax);
MPI_Finalize();
}
It shows no errors, but when i am trying to run the code, this what i have..
[1]: https://i.stack.imgur.com/tl0HF.png
Maybe someone knows hov can i fix it?