It's 2012. I'm writing some code in C. Should I be still be using C89? Are there still compilers that do not support C99?
I don't mind using /* */ instead of //.
I'm not sure about C89 forbids mixing declarations and code. I'm kind of leaning towards the idea that it's actually more readable to have all the declarations in one place, and if it isn't, the function is too long.
VLAs look useful but I haven't needed them yet.
Should I stick with C89 if I don't have a compelling reason not to? Are there other things I haven't considered?
Answer
Unless you know that you cannot use a C99-compatible compiler (the Visual Studio C compiler is the most prominent candidate) there is no good reason for not using the nice things C99 gives you.
However, even if you need to support that compiler you can use some C99 features - just not all of them.
One feature of C99 that is incredibly handy is being able to do for(int i = ...) instead of having to declare your loop variable on top of the function - especially since C actually has a block scope. That's the kind of declaration where having it on top really doesn't improve the readability.