fork2.c

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

int main() {
  pid_t pid;

  switch ((pid = fork())) {
    case -1:
      // error occurred
      printf("Error using fork()");
      break;
    case 0:
      // child process
      printf("In child process:\n");
      printf("\t- pid: %d\n", getpid());
      printf("\t- parent's pid: %d\n", getppid());
      break;
    default:
      // parent process
      printf("In parent process:\n");
      printf("\t- pid: %d\n", getpid());
      printf("\t- child's pid: %d\n", pid);
  }

  return EXIT_SUCCESS;
}