No, my 'intent' is to get: error: signed integer variable used as array index (-Wsigned-index) `int i`: should be `size_t i` error: comparison of signed

No, my 'intent' is to get: error: signed integer variable used as array index (-Wsigned-index) `int i`: should be `size_t i` error: comparison of signed to unsigned integer (-Wsigned-comparison) `i < len`: `i` has type `int`; `len` has type `size_t` Scare quotes on "intent", because I don't write (that particular kind of) obviously broken code in the first place, but the upshot is that i and len both need to be size_t, and anything that lets the compiler obscure that is de facto bad. Edit: previously assumed len was wrong too, but on rereading, you were implying len was already the correct type, and only i was wrong. (Also, the word "variable" is significant; IIRC something like 5+bytecode_next_char promotes to int, but can't actually be negative[1] so shouldn't generate a warning.) 1: Assuming the compiler is configured correctly, ie char is unsigned.