#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
int main(void){ 
  int i, n = 4, status;
  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 */ 
      wait(&status);
      break;
    } else { 
      /* child code  */ 
    }
  /* mutual code */
  printf("This is process %d with parent %d\n",
         getpid(), getppid());
  return 0;
}