Question

What C data type should I use for array indices?

Should it be something like int or long or should it be unsigned int and/or unsigned long?

Answer 1

Atm I always use size_t or unsigned int

Answer 2

If you might have more than 2**32 elements in your array, you need unsigned long, otherwise it would be overkill.

Answer 3

array indices can be negative numbers as well. But you must know that the elements preceding the base element are a part of your array. So it depends on you whether to make the indices unsigned or not.