title: Using pipe to pass integer values between parent and child
body: <p>I'm a little confused on how to properly use pipe() to pass integer values between two processes.</p>
  
  <p>In my program I first create a pipe, then I fork it. I assume I have "Two" pipes then?</p>
  
  <p>From what I understand, this is my assignment. 
  My parent goes through a for loop checking an integer value "i" for a certain operation, increases a count variable, and saves value into an array. After each check my parent should pass an integer value, "i" to my child through a pipe. My child then uses that integer value, does some check on the value, and should increase a count variable, and save the result in a [shared?] array. Eventually; the child should return it's final count to the parent, who then prints out the two counts, and the "Shared" array.</p>
  
  <p>-> I'm not sure I need to have a shared array or to save the results at all. I may only need the counts - the homework was ambiguous and I'm awaiting a response from the professor. Also; can I even do a shared array between processes? It sounds like a start of some problem to me.</p>
  
  <p>-> Here are my questions:
  One; how do I use pipes for integers? I've only seen them for character arrays and previous answers don't seem to think this is possible or legal..? I'm not sure. There was no resolution that I could find on it.</p>
  
  <p>-> How do I use a unidirectional pipe to pass integers to a child? And have the child return something? I'm not sure how I'm able to... differentiate between the two pipes. I do "know" [or think I know] that I have to close one unused portion of each pipe to avoid "Some vague problem". </p>
  
  <p>Sorry for the dumb questions; I haven't been taught processes (aside from fork) or pipes (at all) yet in this class - so I'm not really sure where to start!</p>
  
  <p>Heres parts of my code - it's not pretty and it doesn't work and I don't expect it to. It's more of a shell placeholder. Once I figure out how to use a pipe - I'd Probably make the code make sense.</p>
  
  <pre><code>int main(void)
  {
  int fd[2];
  pid_t childpid;
  pid_t parentpid;
  int i;
  int threecount = 0;
  int fivecount = 0;;
  int results [MAXSIZE];
  
  parentpid = getpid(); //Get current process ID number
  
  pipe(fd);
  childpid = fork(); 
  
  if(childpid == 0){
  close(fd[0]); //Closing this for some other reason
  
  }
  int j = 0;
  
  if(childpid &gt; 0)
  close(fd[1]); //Closing this for some reason
  
  
  if( childpid == -1 )
  {
      perror("Failed to fork\n");
      return 1;
  }
  if (childpid &gt; 0)
  {
      for(i = 1; i &lt; MAXSIZE;i++)
      {
          if(i % 5 == 0)
          {
              fivecount++;
              i = results[j];
              j++; 
              wait(NULL);
          }
      }
  }
  else if (childpid == 0)
      {
          if(i % 3 == 0) //This i here should probably be the i value above, piped to the child
          {
              threecount++;
              i = results[j];  //This should be part of th pipe
              j++;    //Trying to keep count of that shared array, not really the right way to do it though.
          }
  
      }
      printf("%d  %d  \n", fivecount,threecount);
      return 0;
  </code></pre>
  
  <p>}</p>