A size_t is an unsigned integral type which is the result of the sizeof operator. The two are designed to go together. To me it's the type most suited to indexing an array (you don't need negative indexes, do you?).

Sure you could use an int and it will be correct 99.999% of the time -- I was just going for 100%. Plus, with an array of ints, I find it easier to see the index from the data if they're not just slopped together.