I agree with the other commenter about the comma in this sentence. But I'd also like to point out that 100% error-free code is possible. There's a whole branch of computer science dedicated to it: formal verification. I personally have used Coq to write certified code in the past, and I'm quite confident that my code was 100% error-free.

Of course, there are some qualifications one should make regarding such a claim: you have to trust that your specification is "correct", that your hardware is functioning correctly, that the proof checker didn't accept a bogus proof, that the underlying logic (e.g., the calculus of inductive constructions) is consistent, etc. That's a lot of things to trust, but the point is that you don't have to trust yourself.