c - Why doesn't MPI_SEND work within my for loop? It works fine if explicitly stated -

i'm trying send number p-1 processes. process 0 sends value other processes. use mpi_send command this. when explicitly write out mpi_send commands 3 processes, works fine. when want put in loop, gives me output segmentation fault code. here code:

#include <stdlib.h> #include <mpi.h> #include "a1.h"  //authors //lakshan sivananthan - 1150161 //razmig papissian - 1152517  int main(int argc, char** argv) {   rgb *image;   int width, height, max;   int windowlength = atoi(argv[3]);   int my_rank, p, local_height, source, i;    int dest;    mpi_status status;    mpi_init(&argc, &argv);   mpi_comm_size(mpi_comm_world, &p);   mpi_comm_rank(mpi_comm_world, &my_rank);    int *processorrows;   processorrows = (int*)malloc(sizeof(int)*(p+1));    if (my_rank == 0) {      printf("process %d reading...\n", my_rank);     image = readppm(argv[1], &width, &height, &max);       //calculate rows each process      (i=0; i<p; i++) {        processorrows[i] = height/p;      }      (i=0; i< height%p; i++){        processorrows[i]++;     }      (dest=1; dest<p; dest++) {        mpi_send(processorrows + dest, 1, mpi_int, dest, 0, mpi_comm_world);       //mpi_send(processorrows + 2, 1, mpi_int, 2, 0, mpi_comm_world);       //mpi_send(processorrows + 3, 1, mpi_int, 3, 0, mpi_comm_world);     }    }   else {      mpi_recv(processorrows, 1, mpi_int, 0, 0, mpi_comm_world, &status);     printf("i process %d , run %d rows...\n", my_rank, *processorrows);    }     //processimage(width, height, image, windowlength);   //writeppm(argv[2], width, height, max, image);    free(image);   free(processorrows);    mpi_finalize();   return(0);  } 

if remove loop, replace "dest" 1, , uncomment other 2 mpi_send lines, works fine when running mpirun -np 4 ./program

not sure what's going on here...

i'm not sure trying accomplish. but, statement

process 0 sends value other processes.

and part of code, expect scatter process-0 other pes rather send-receive loop tricks.

remove send-receive pairs , remove loops, use single scatter operation. here link mpi_scatter operation https://www.open-mpi.org/doc/v1.8/man3/mpi_scatter.3.php. if unsure scatter operation, have @ neat explanation http://mpitutorial.com/tutorials/mpi-scatter-gather-and-allgather/

it looks like, size of processorrows array size of total number of process used. and, trying send each element of processorrows array other ranks. hence, code should 1 below:

int *processorrows; processorrows = (int*)malloc(sizeof(int)*(p+1));  if (my_rank == 0) {     printf("process %d reading...\n", my_rank);     image = readppm(argv[1], &width, &height, &max);       (i=0; i<p; i++) {         processorrows[i] = height/p;     }      (i=0; i< height%p; i++){         processorrows[i]++;     } }    mpi_scatter(processorrows, 1, mpi_int, processorrows, 1, mpi_int, 0, mpi_comm_world);