fork system call

#include <stdio.h>
#include <unistd.h>

int main()
{
	fork();
	fork();
	puts("Hi");
	return 0;
}

// Output:
// Hi
// Hi
// Hi
// Hi

#include <stdio.h>
#include <unistd.h>

int main()
{
	fork();
	puts("Hi");
	return 0;
}

// Output:
// Hi
// Hi

System call fork() is used to create processes. It takes no arguments and 
returns a process ID.
The purpose of fork() is to create a new process, which becomes the child 
process of the caller.
After a new child process is created, both processes will execute 
the next instruction following the fork() system call.

#include <stdio.h>
#include <unistd.h>

int main()
{
	fork();
	fork();
	fork();
	puts("Hi");
	return 0;
}

// Output:
// Hi
// Hi
// Hi
// Hi
// Hi
// Hi
// Hi
// Hi

int counter = 0;
int main()
{
  int i;
  for (i = 0; i < 2; i ++){
    fork();
    counter++;
    printf("counter = %d\n", counter);
  }
  printf("counter = %d\n", counter);
  return 0;
}