Ask HN: Using C99 or C11? What is your impression?

I'm interested because I've mainly used ANSI C (pre-99), so like to know the experiences of those using higher versions of the C standard like 11 and 99.

I know about Rust, D, Zig, Nim, and have used D some.

This question is more about the old C vs. the newer standards, but feel free to talk about those other languages too, if you have any relevant points to make.