Strangely enough, I often find my self impulsively writing (n & 1) to check for even/odd numbers. It just feels natural to me -- maybe because the first C programs I wrote were for µCs, where this kind of bit-twiddling tends to be used everywhere, and, correspondingly, people know what (n & 1) does. Sure enough, even on microcontrollers (n % 2) has no overhead compared to (n & 1) when optimisations are turned on.
It only ever caught my attention that writing (n & 1) is weird when some TAs looking at my code didn't understand what I was doing during my first college year.
It feels natural to me...but I also like writing emulators, so I've probably got more experience in common with µC devs than most other software developers do.
It feels natural to anyone who understands binary numbers. Every odd number in binary will have the last bit as 1. Just like in the decimal system, every number that is a multiple of 10 will has the last digit as 0. If you want to see if a number is a multiple of ten, I guess you could do a mod 10 of the number and see if the remainder is 0. But if you understand the decimal system, you would just naturally check if the last digit is 0.
It only ever caught my attention that writing (n & 1) is weird when some TAs looking at my code didn't understand what I was doing during my first college year.