#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int main()
{
  int x = 100;
  pid_t pid;  /* process id */

  /* fork a child process */
  pid = fork();  /*** fork() returns twice... ***/

  if ( pid < 0 ) {
    fprintf( stderr, "ERROR: fork() failed.\n" );
    exit( 1 );
  }

  if ( pid == 0 )  /* child */
  {
    printf( "CHILD: I'm new. Let me look around.\n" );

    x++;
    printf( "CHILD: x is %d\n", x );
    exit( 7 );

  }
  else /* parent (pid > 0) */
  {
    int status;  /* return status from the child process */
    pid_t child_pid;

    printf( "PARENT: created process id %d\n", pid );

    /* wait until child terminates */
    child_pid = wait( &status );
    printf( "PARENT: child process id %d terminated", child_pid );

    /* least-significant byte is non-zero if child terminated abnormally */
    /* 00000000 00000000 00000111 00000000 */
    if ( ( status & 0x000F ) != 0 ) {
      printf( " abnormally.\n" );
    } else {
      int rc = status >> 8;  /* shift right 8 bits */
      rc = rc & 0x00FF;  /* mask most-significant bytes */
      printf( " with exit status %d.\n", rc );
    }

    printf( "PARENT: x is %d\n", x );
  }

  return 0;
}