adjust printf, use unsigned output

src/counter.c

@@ -72,6 +72,6 @@ int main (void) {
     pthread_mutex_unlock(&counterMutex);
 
     double f = 1.0 / (((double) my_diff) / 1000000.0);
-    printf("%d %d %d %f\n", my_ec, my_counter, my_diff, f);
+    printf("%u %u %u %f\n", my_ec, my_counter, my_diff, f);
   }
 }