fork1.c

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

int main() {
  pid_t pid;

  if ((pid = fork()) < 0) {
    // error occurred
    printf("Error using fork()");
    return EXIT_FAILURE;
  } else if(pid == 0) {
    // child process
    printf("In child process:\n");
    printf("\t- pid: %d\n", getpid());
    printf("\t- parent's pid: %d\n", getppid());
  } else {
    // parent process
    printf("In parent process:\n");
    printf("\t- pid: %d\n", getpid());
    printf("\t- child's pid: %d\n", pid);
  }

  return EXIT_SUCCESS;
}