Strange behaviour setting pinMode by array

[serious_sam]

@gcjr

#undef MyHW
#ifdef MyHW
byte PINS[] = { 10, 11, 12, 13 };
#else
byte PINS[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
#endif

I'm sorry, I don't understand this part of your code. I'm just beginning. Could you please explain ?