From one of his other blogposts. "Guidelines for computing sizes and subscripts"

  Never mix unsigned and signed operands. Prefer signed. If you need to convert an operand, see (2).

https://www.youtube.com/watch?v=wvtFGa6XJDU

Skeeto and Stroustrup are a bit confused about valid index types. They prefer signed, which will lead to overflows on negative values, but have the advantage of using only half of the valid ranges, so there's more heap for the rest. Very confused