mpiReduce

#include <mpi.h>
#include <iostream>
#include <sstream>
using namespace std;

void myFunc(long long int *inp, long long int *inout, int *n, MPI_Datatype *type) {
    for (int i=0; i<*n; i++) {
        long long int mod = 10;
        while (mod <= inout[i]) mod*=10;
        inout[i] += inp[i]*mod;
        stringstream buf;
        buf << inout[i] << endl;
        cout << buf.str();
    }
}

int main(int argc, char *argv[])
{
    int myrank, tag = 0;
    MPI_Status status;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

    long long int myData[] = {myrank+1};
    long long int result[1] = {-1};
    MPI_Op myOp;
    MPI_Op_create((MPI_User_function*)myFunc, true, &myOp);
    MPI_Reduce(myData, result, 1, MPI_LONG, myOp, 0, MPI_COMM_WORLD);

    if (myrank == 0) cout << result[0] << endl;

    MPI_Op_free(&myOp);
    MPI_Finalize();
    return 0;
}