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

void fork0() {
  pid_t pid = fork();
  if (pid == 0) {
    printf("hello from child\n");
  } else {
    printf("hello from parent\n");
  }
}

void fork1()
{
    int x = 1;
    pid_t pid = fork();
    if (pid == 0) {
	printf("Child has x = %d\n", ++x);
    } else {
	printf("Parent has x = %d\n", --x);
    }
    printf("Bye from process %d with x = %d\n", getpid(), x);
}

void fork2()
{
    printf("L0\n");
    fork();
    printf("L1\n");    
    fork();
    printf("Bye\n");
}

void fork3()
{
    printf("L0\n");
    fork();
    printf("L1\n");    
    fork();
    printf("L2\n");    
    fork();
    printf("Bye\n");
}

void fork4()
{
    printf("L0\n");
    if (fork() != 0) {
	printf("L1\n");    
	if (fork() != 0) {
	    printf("L2\n");
	    fork();
	}
    }
    printf("Bye\n");
}

void fork5()
{
    printf("L0\n");
    if (fork() == 0) {
	printf("L1\n");    
	if (fork() == 0) {
	    printf("L2\n");
	    fork();
	}
    }
    printf("Bye\n");
}


void cleanup(void) {
   printf("cleaning up\n");
}

void fork6() {
   atexit(cleanup);
   fork();
   exit(0);
}

#define N 10
void fork10()
{
    pid_t pid[N];
    int i;
    int child_status;
    for (i = 0; i < N; i++)
	if ((pid[i] = fork()) == 0)
	    exit(100+i); /* Child */
    for (i = 0; i < N; i++) {
	pid_t wpid = wait(&child_status);
	if (WIFEXITED(child_status))
	    printf("Child %d terminated with exit status %d\n",
		   wpid, WEXITSTATUS(child_status));
	else
	    printf("Child %d terminate abnormally\n", wpid);
    }
}

void fork11()
{
    pid_t pid[N];
    int i;
    int child_status;
    for (i = 0; i < N; i++)
	if ((pid[i] = fork()) == 0)
	    exit(100+i); /* Child */
    for (i = N-1; i >= 0; i--) {
	pid_t wpid = waitpid(pid[i], &child_status, 0);
	if (WIFEXITED(child_status))
	    printf("Child %d terminated with exit status %d\n",
		   wpid, WEXITSTATUS(child_status));
	else
	    printf("Child %d terminated abnormally\n", wpid);
    }
}



int run(int choice) {
  switch (choice) {
  case 0:
    fork0();
    break;
  case 1:
    fork1();
    break;
  case 2:
    fork2();
    break;
  case 3:
    fork3();
    break;
  case 4:
    fork4();
    break;
  case 5:
    fork5();
    break;
  case 6:
    fork6();
    break;
  case 10:
    fork10();
    break;
  case 11:
    fork11();
    break;
  default:
    printf("Unknown option %d\n", choice);
    break;
  }
}

int main(int argc, char *argv[]) {
  if (argc != 2)
    printf("Must give argument\n");
  int c = atoi(argv[1]);
  printf("\nRunning fork%d\n", c);
  run(c);
  return 0;
}