#include <stdio.h>

void val_incr(int counter);
void ref_incr(int *counter);

int main(void) {
  int counter = 9;

  printf("main: at startup, counter is %d\n", counter);
  val_incr(counter);
  printf("main: after val_incr, counter is %d\n", counter);
  ref_incr(&counter);
  printf("main: after ref_incr, counter is %d\n", counter);
  return 0;
}

void val_incr(int counter) {
  printf("val_incr: start, counter is %d\n", counter);
  counter++;
  printf("val_incr: exit, counter is %d\n", counter);
}

void ref_incr(int *counter) {
  printf("ref_incr: start, counter is %d\n", *counter);
  (*counter)++;
  printf("ref_incr: exit, counter is %d\n", *counter);
}