#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
int x = 1, y = 2, z = 3;
sem_t semXY;
sem_t semZ;
void* a(void* param){
  int i = 0;
  while(1){
    x = x + x;
    y = y + y;
    sem_post(&semXY);
    sem_wait(&semZ);
    printf("%d - %d = %d\n", y, x, z);
    if(++i == 1) break;
  }
  return 0;
}
void* b(void* param){
  int i = 0;
  while(1){
    sem_wait(&semXY);
    z = y - x;
    sem_post(&semZ);
    if(++i == 1) break;
  }
  return 0;
}
int main(){
   pthread_t nitA, nitB;

   sem_init(&semXY, 0, -1);
   sem_init(&semZ, 0, 0);

   pthread_create(&nitA, 0, a, 0);
   pthread_create(&nitB, 0, b, 0);

   pthread_join(nitA, 0);
   pthread_join(nitA, 0);

   sem_destroy(&semXY);
   sem_destroy(&semZ);

   return 0;
}