The other comment mentions tests, but I'd like to that to that. The reason why it's impossible for anyone, even the single greatest programmer on the planet, to not create bugs, is due to the high complexity of the software we write. It's not so much that you'll make a mistake when creating a new program. It's that over time, as you make more and more changes, it's impossible to actually trace out the exponential complexity that arises from your changes.
The purpose of unit tests is to catch these, and yes as you mention lower down even those aren't 100% infallible but they greatly help. That's why even with some of the greatest programmers and extensive testing, we still constantly see major bugs from every single top tech company. I don't think there exists a single completely bug-free software of non-negligible size out there.
The purpose of unit tests is to catch these, and yes as you mention lower down even those aren't 100% infallible but they greatly help. That's why even with some of the greatest programmers and extensive testing, we still constantly see major bugs from every single top tech company. I don't think there exists a single completely bug-free software of non-negligible size out there.