MPI Parallel Search - Prime

The following code prints the first prime number occurring in the array.

	/***************************************
	AUTHOR: ANKIT MAHATO
	amahato@iitk.ac.in
	IIT KANPUR
	This code distributes data and search
	for the prime number which occurs first.
	The root and other process codes can be
	clubbed together but in this code root
	has been treated separately so as for
	better understanding.
	***************************************/
	#include "mpi.h"
	#include <stdio.h>
	#include <math.h>
	#include <stdlib.h>
	#define MASTER 0
	int IS_prime(int *num)
	{
	int isprime = 0;
	int i;
	if(*num==2)
	return 0;
	if(*num%2==0)
	return 1;
	for(i = 3; i <= (int)sqrt(*num); i+=2)
	{
	if((*num% i) == 0)
	{
	isprime = 1;
	break;
	}
	}
	return isprime;
	}
	int main (int argc, char *argv[])
	{
	int * a;
	int * c;
	// arrays a and c
	int total_proc;
	// total nuber of processes
	int rank;
	// rank of each process
	int T;
	// total number of test cases
	long long int n_per_proc;
	// elements per process
	long long int i, n;
	MPI_Status status;
	// Initialization of MPI environment
	MPI_Init (&argc, &argv);
	MPI_Comm_size (MPI_COMM_WORLD, &total_proc);
	//Now you know the total number of processes running in parallel
	MPI_Comm_rank (MPI_COMM_WORLD,&rank);
	//Now you know the rank of the current process
	int * ap;
	if (rank == MASTER) //you choose process rank 0 to be your root which will be used to perform input output.
	{
	scanf ("%d", &T);
	// you get the total number of test cases
	MPI_Bcast (&T, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
	// Then you broadcast it to every process out there
	while (T--)
	{
	scanf ("%lld", &n);
	a = (int *) malloc(sizeof(int)*n);
	c = (int *) malloc(sizeof(int)*total_proc);
	MPI_Bcast (&n, 1, MPI_LONG_LONG_INT, MASTER, MPI_COMM_WORLD);
	n_per_proc = n/total_proc;
	for(i=0;i<n;i++)
	scanf ("%d", &a[i]);
	if(n%total_proc != 0)
	{
	n_per_proc+=1;
	for(i=0;i<(n_per_proc*total_proc - n);i++)
	a[n+i] = 0;
	} // to divide data evenly by the number of processors
	ap = (int *) malloc(sizeof(int)*n_per_proc);
	int cp;
	MPI_Bcast (&n_per_proc, 1, MPI_LONG_LONG_INT, MASTER, MPI_COMM_WORLD);
	//Broadcast element per process
	MPI_Scatter(a, n_per_proc, MPI_INT, ap, n_per_proc, MPI_INT, 0, MPI_COMM_WORLD);
	//scattering array a
	for(i=0;i<n_per_proc;i++)
	{
	if(IS_prime(&ap[i])==0)
	{
	cp=ap[i];
	break;
	}
	if(i==(n_per_proc-1))
	cp=-1;
	}
	MPI_Gather(&cp, 1, MPI_INT, c, 1, MPI_INT, MASTER, MPI_COMM_WORLD); //gathering array c
	for(i=0;i<total_proc;i++)
	{
	if(c[i]==-1)
	continue;
	else
	{
	printf ("%d\n", c[i]);
	break;
	}
	}
	}
	}
	else
	{ // Non-master tasks
	// Receive T
	MPI_Bcast (&T, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
	//printf("%d from process %d\n",T,rank);
	while (T--)
	{
	MPI_Bcast (&n, 1, MPI_LONG_LONG_INT, MASTER, MPI_COMM_WORLD);
	MPI_Bcast (&n_per_proc, 1, MPI_LONG_LONG_INT, MASTER, MPI_COMM_WORLD);
	ap = (int *) malloc(sizeof(int)*n_per_proc);
	int cp;
	MPI_Scatter(a, n_per_proc, MPI_INT, ap, n_per_proc, MPI_INT, 0, MPI_COMM_WORLD);
	//Recieving Scattered a
	for(i=0;i<n_per_proc;i++)
	{
	if(IS_prime(&ap[i])==0)
	{
	cp=ap[i];
	break;
	}
	if(i==(n_per_proc-1))
	cp=-1;
	}
	MPI_Gather(&cp, 1, MPI_INT, c, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
	//To initiate the gathering of first occurred primes from all processes
	//If no prime number in the process then -1 is returned
	}
	}
	MPI_Finalize();
	//Terminate MPI Environment
	return 0;
	}

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