MPI sum of array receive working for only one rank - c

Question

I am trying to find the sum of an array of length 100 elements using MPI, under the restrictions of only using MPI_Send and MPI_receive , the code that I have written finds the sum of each processor but during the re-send to the main processor(rank=0) my code only receives from one processor
My Code
#include "stdafx.h"
#include <stdio.h>
#include <string.h>
#include "mpi.h"
#include "math.h"
int val = 1;
int main(int argc, char* argv[]) {
int my_rank;
int p;
int ierr;
int i;
int a[100];
int q=0;
for (i = 0; i <100; i++)
{
a[i] = i+1;
}
int send,recv;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &p);
int part = 100 /(p-1);
if (my_rank == 0)
{
for (i = 1; i < p; i++)
{
send = part * (i-1);
MPI_Send(&send, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
}
}
else
{
MPI_Recv(&recv, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
for (i = recv; i < recv + part; i++)
{
val = val+a[i];
}
printf("%d\n", val);
MPI_Send(&val, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
}
if (my_rank == 0)
{
MPI_Recv(&val, 1, MPI_INT, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status);
printf("%d", val);
q = q + val;
}
MPI_Finalize();
if (my_rank == 0)
{
printf("The output is %d\n", q);
}
return 0;
}
My output
where am i going wrong

Answer 1

Because you only recieve the result from one process. To recieve all results, iterate over process ranks:
if (my_rank == 0)
{
for (rank = 1; rank < proc_cnt; rank++)
{
MPI_Recv(&val, 1, MPI_INT, rank, 0, MPI_COMM_WORLD, &status);
printf("value of rank %d is %d", rank, val);
q = q + val;
}
}
Ordinarily, this a bad practice and may lead to deadlocks. Use mpi_gather() if allowed.