I have a large number that loops from 0 to 65535 (I chose 16 bits simply to have a nice cutting off point). I'm incrementing an int, and there's an if statement that checks if the int is 65536. If it is, it sets the int to 0; a little kludgy, but it works. I know it would be much more efficient to just use a short int and let it overflow, but I initially didn't do that because a short is not guaranteed to be 2 bytes, it's just fairly likely.
This is C code running on a linux (ubuntu) machine. If I were to use a short and later decided to run this program on another OS (or say, run it on a 64-bit machine, since I'm testing on a 32-bit one now), is there a pretty good chance that my short will still be 2 bytes? I can easily test it on a few different machines, but some of the people here have worked with a LOT of computers. Is there a terrible pitfall I should be watching out for?
There is no guarantee of the size of any of the built-in types like int, char and the like. (See for example this question, which is about C++, but is also accurate for C as far as I know in this regard)
If you need fixed-size integer types, include C99's <stdint.h> and use the fixed-width typesdefined there.