#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
int main(void){
  int i, n = 4;
  pid_t childpid;
  for (i = 1; i < n;  ++i)
    if((childpid = fork()) < 0){ 
      /* fork error */
      perror("error in fork"); 
      exit(EXIT_FAILURE); 
    } else if(childpid){ 
      /* parent code */ 
       break;
    } else { 
      /* child code */ 
    } 
  /* mutual code */ 
  printf("This is process %ld with parent %ld\n",
         (long)getpid(), (long)getppid());
  return 0;
}