Variable Sized Arrays in C

Question

I guess my question is whether the following is valid C

int main(void) {
  int r = 3;
  int k[r];
  return 0;
}

If so, would some one care to explain why it does not work in Microsoft's C compiler, but in GCC, and when it was added to the C standard.

Thank you

Answer 1

It is in C99. MSVC only supports C89.

Answer 2

The C99 standard added variable-length arrays, but other vendors such as GCC added them much earlier.