#include <stdatomic.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

atomic_int i = 0;
void* thread_func(void* arg) {

  int local, new;
  do {
    local = atomic_load(&i);
    new = (local + 1) % 16;
  } while (!atomic_compare_exchange_strong(&i, &local, new));

  printf("%i: %i\n", (int)arg, new);
}
int main(void) {
  pthread_t id[20];
  for (int i = 0; i < 20; i++) {
    // korrekt mit free
    int* idref = malloc(sizeof(id));
    *idref = i;
    pthread_create(&id[i], NULL, thread_func, (void*)i); // (void*)i ist verboten!
  }
  
  
}