Visual Studio 2012 for Windows Desktopで配列の添字を省略できるかどうかを確認してみた。 →[]でも[0]でも結果は変わらず。

a.c

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

struct A
{
  int i[];
};

int main(int argc, char *argv[])
{
  struct A *a = malloc(sizeof (struct A) + sizeof (int) * 3);
  a->i[0] = 0;
  a->i[1] = 1;
  a->i[2] = 2;
  printf("%d %d %d\n", a->i[0], a->i[1], a->i[2]);
  free(a);
  return 0;
}

a.cのコンパイルと実行の結果

>cl a.c
Microsoft(R) C/C++ Optimizing Compiler Version 17.00.60204.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

a.c
Microsoft (R) Incremental Linker Version 11.00.60204.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:a.exe
a.obj

>a.exe
0 1 2