C under Ubuntu - not expected result trying to solve "Wheel game"

The wheel. The main process (A) will create a subprocess (B) that will create another subprocess (C). Then the main process (A) will send the generate a random number (between 1000 and 2000) to process B. The process B will subtract 10 units and will send the number to process C. C will subtract 20 units and will send the number to A. The A process will subtract 30 units and will send the number to B, again. And so on, until the values is less than zero. In this moment the game will stop. The winner is the process that established the negative number.

The communication between all the processes are done using pipe channels.

My solution was:

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


int pass(char* id, int in, int out, int x)
{
  int n;
  read(in, &n, sizeof(int));
  printf("%s %d\n", id, n);
  n=n-x;
  printf("x= %d\n", x);
  write(out, &n, sizeof(int));
  return n;
}


void closeall(int* a, int* b, int* c)
{
  close(a[0]);
  close(a[1]);
  close(b[0]);
  close(b[1]);
  close(c[0]);
  close(c[1]);
}



int main()

{
  int a2b[2], b2c[2], c2a[2], n, x;
  pipe(a2b);
  pipe(b2c);
  pipe(c2a);

  srand(time(NULL));
  n=rand() % 1001 + 1000;
  x=0;

  write(c2a[1], &n, sizeof(int));

  if (fork() == 0){
    while (pass("grandfather ", c2a[0], a2b[1], x) > 0){
            x=x+10;}
    exit(0);

  }

  if (fork() == 0){
    while (pass("father ", a2b[0], b2c[1], x) > 0){
        x=x+10;}
    exit(0);
  }


  if (fork() == 0){
    while (pass("child ", b2c[0], c2a[1], x) > 0){
        x=x+10;}
    exit(0);
  }

  closeall(a2b, b2c,c2a);

  wait(0);
  wait(0);
  wait(0);
  return 0;
}

After running the program the result was

grandfather  1420
x= 0
father  1420
x= 0
child  1420
x= 0
grandfather  1420
x= 10
father  1410
x= 10
child  1400
x= 10
grandfather  1390
x= 20
father  1370
x= 20
child  1350
x= 20
grandfather  1330
x= 30
father  1300
x= 30
child  1270
x= 30
grandfather  1240
x= 40
father  1200
x= 40
child  1160
x= 40
grandfather  1120
x= 50
father  1070
x= 50
child  1020
x= 50
grandfather  970
x= 60
father  910
x= 60
child  850
x= 60
grandfather  790
x= 70
father  720
x= 70
child  650
x= 70
grandfather  580
x= 80
father  500
x= 80
child  420
x= 80
grandfather  340
x= 90
father  250
x= 90
child  160
x= 90
grandfather  70
x= 100
father  -30
x= 100
child  -130
x= 100

Can someone help me improve the source code in order to obtain the correct result? As seen before, the subtracted value of x is the same for three times, and it doesn't stop after the first negative number.