title: fork() and wait() calls
body: <p>I have a question about the following code. This is an example found on <a href="http://www.csl.mtu.edu/cs4411.ck/www/NOTES/process/fork/wait.html" rel="nofollow">this page</a>, not my code.</p>
  
  <p>The parent process forks 2 child processes, each of them counting to 200 then exiting. What I don't understand is why aren't the children printing their messages immediately after they are forked and they allow their father to enter waiting status?
  Also, how is the wait system call returning the pid of the child that finishes first? </p>
  
  <p><strong>pid = wait(&amp;status);</strong></p>
  
  <pre><code>#include  &lt;stdio.h&gt;
  #include  &lt;string.h&gt;
  #include  &lt;sys/types.h&gt;
  
  #define   MAX_COUNT  200
  #define   BUF_SIZE   100
  
  void  ChildProcess(char [], char []);    /* child process prototype  */
  
  void  main(void)
  {
       pid_t   pid1, pid2, pid;
       int     status;
       int     i;
       char    buf[BUF_SIZE];
  
       printf("*** Parent is about to fork process 1 ***\n");
       if ((pid1 = fork()) &lt; 0) {
            printf("Failed to fork process 1\n");
            exit(1);
       }
       else if (pid1 == 0) 
            ChildProcess("First", "   ");
  
       printf("*** Parent is about to fork process 2 ***\n");
       if ((pid2 = fork()) &lt; 0) {
            printf("Failed to fork process 2\n");
            exit(1);
       }
       else if (pid2 == 0) 
            ChildProcess("Second", "      ");
  
       sprintf(buf, "*** Parent enters waiting status .....\n");
       write(1, buf, strlen(buf));
       pid = wait(&amp;status);
       sprintf(buf, "*** Parent detects process %d was done ***\n", pid);
       write(1, buf, strlen(buf));
       pid = wait(&amp;status);
       printf("*** Parent detects process %d is done ***\n", pid);
       printf("*** Parent exits ***\n");
       exit(0);
  }
  
  void  ChildProcess(char *number, char *space)
  {
       pid_t  pid;
       int    i;
       char   buf[BUF_SIZE];
  
       pid = getpid();
       sprintf(buf, "%s%s child process starts (pid = %d)\n", 
               space, number, pid);
       write(1, buf, strlen(buf));
       for (i = 1; i &lt;= MAX_COUNT; i++) {
            sprintf(buf, "%s%s child's output, value = %d\n", space, number, i); 
            write(1, buf, strlen(buf));
       }
       sprintf(buf, "%s%s child (pid = %d) is about to exit\n", 
               space, number, pid);
       write(1, buf, strlen(buf));     
       exit(0);
  }
  </code></pre>
  
  <p>Output for MAX_COUNT 40.</p>
  
  <pre><code>*** Parent is about to fork process 1 ***
  *** Parent is about to fork process 2 ***
  *** Parent enters waiting status .....
     First child process starts (pid = 3300)
     First child's output, value = 1
        Second child process starts (pid = 3301)
        Second child's output, value = 1
     First child's output, value = 2
        Second child's output, value = 2
        Second child's output, value = 3
     First child's output, value = 3
        Second child's output, value = 4
     First child's output, value = 4
        Second child's output, value = 5
     First child's output, value = 5
        Second child's output, value = 6
     First child's output, value = 6
        Second child's output, value = 7
     First child's output, value = 7
        Second child's output, value = 8
     First child's output, value = 8
        Second child's output, value = 9
     First child's output, value = 9
        Second child's output, value = 10
     First child's output, value = 10
        Second child's output, value = 11
     First child's output, value = 11
        Second child's output, value = 12
     First child's output, value = 12
        Second child's output, value = 13
     First child's output, value = 13
        Second child's output, value = 14
     First child's output, value = 14
        Second child's output, value = 15
     First child's output, value = 15
        Second child's output, value = 16
     First child's output, value = 16
        Second child's output, value = 17
     First child's output, value = 17
        Second child's output, value = 18
     First child's output, value = 18
        Second child's output, value = 19
     First child's output, value = 19
        Second child's output, value = 20
     First child's output, value = 20
        Second child's output, value = 21
     First child's output, value = 21
        Second child's output, value = 22
     First child's output, value = 22
        Second child's output, value = 23
     First child's output, value = 23
        Second child's output, value = 24
     First child's output, value = 24
        Second child's output, value = 25
     First child's output, value = 25
        Second child's output, value = 26
     First child's output, value = 26
        Second child's output, value = 27
     First child's output, value = 27
        Second child's output, value = 28
     First child's output, value = 28
        Second child's output, value = 29
     First child's output, value = 29
        Second child's output, value = 30
     First child's output, value = 30
        Second child's output, value = 31
     First child's output, value = 31
        Second child's output, value = 32
     First child's output, value = 32
        Second child's output, value = 33
     First child's output, value = 33
        Second child's output, value = 34
     First child's output, value = 34
        Second child's output, value = 35
     First child's output, value = 35
        Second child's output, value = 36
     First child's output, value = 36
        Second child's output, value = 37
     First child's output, value = 37
        Second child's output, value = 38
     First child's output, value = 38
        Second child's output, value = 39
     First child's output, value = 39
        Second child's output, value = 40
     First child's output, value = 40
        Second child (pid = 3301) is about to exit
     First child (pid = 3300) is about to exit
  *** Parent detects process 3300 was done ***
  *** Parent detects process 3301 is done ***
  *** Parent exits ***
  </code></pre>
  
  <p>Why     <code>*** Parent enters waiting status .....</code> line is displayed at the beginning and not somewhere after the childs start printing?</p>