//
// Written for Computer Networks and Systems lab classes
// AUTHOR : Sergiusz Warga

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include <sys/wait.h>

#define N_OF_ELEMENTS 1e6
#define N_OF_CHILDREN 10
#define SPAN (int)(N_OF_ELEMENTS/N_OF_CHILDREN)

int child_task(int * array, int start) {
    int sum = 0;
    for (int i = start; i < start + SPAN; ++i ) {
        sum += array[i];
    }
    return (int)(sum/SPAN);
}

int avg(int * array) {
    int sum = 0;
    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        sum += array[i];
    }
    return sum/N_OF_CHILDREN;
}

int main() {
    srandom(time(NULL));
    int status[N_OF_CHILDREN];
    int sums[N_OF_CHILDREN] = {0};
    int children_pids[N_OF_CHILDREN];
    int * array = malloc(N_OF_ELEMENTS * sizeof(int));

    for (int i = 0; i < N_OF_ELEMENTS; ++i) {
        array[i] = random() % 101;
    }

    pid_t pid;

    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        pid = fork();
        if (pid == -1) {    // If something went wrong.
            perror("Fork: ");
            exit(EXIT_FAILURE);
        }
        if (pid == 0){      // If this is a child process.
            int sum = child_task(array, (int)(i*SPAN));
            exit(sum);
        }
        children_pids[i] = pid;
    }

    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        waitpid(children_pids[i], &status[i], 0);
        sums[i] = WEXITSTATUS(status[i]);
    }

    printf("%d\n", avg(sums));

    return 0;
}