#include <stdio.h>

// struct with only an array
struct StructOfArray {
  int c[3];
};

struct S {
  int x;
};

void foo(struct StructOfArray a) {
  a.c[0] += 1;
}

void bar(struct S ar[]) {
  struct S new; new.x = ar[0].x+1;
  ar[0] = new;
}

int main() {
  struct StructOfArray a;
  a.c[0] = 1;
  a.c[1] = 2;
  a.c[2] = 3;

  printf("%d\n", a.c[0]);  // 1
  foo(a);
  printf("%d\n", a.c[0]);  // 1, so pass struct including array by copy

  // array with just one struct
  struct S sa[1];
  sa[0].x = 1;
  printf("%d\n", sa[0].x);  // 1
  bar(sa);
  printf("%d\n", sa[0].x);  // 2, so pass array of structs by reference
}