// Create a program that creates a child process using fork.
// The parent and child processes should count from 0 to N, printing every STEP.
// N and step are supplied via command line arguments.
#include <stdio.h>
#include <stdlib.h> // exit
#include <unistd.h> // fork, sleep
#include <sys/wait.h> // wait

int count(char *who, int n, int step){
    // count from 0 to print every step
    for (int i = 0; i <= n; i++){
        if (i % step == 0) 
            printf("%s:\t%d\n", who, i);
    }
    return 0;
}

int main(int argc, char *argv[]){
    if (argc != 3){
        printf("Usage: %s N STEP\n", argv[0]);
        exit(1);
    }

    int N = atoi(argv[1]);
    int STEP = atoi(argv[2]);   
    int status;
    int pid;

    if ((pid = fork()) == 0){
        count("child", N, STEP);
        exit(0);
     }
    else if (pid == -1){
        printf("fork failed.\n");    
        exit(2);
    }

    count("parent", N, STEP);
    return 0;
}