As someone who writes both C++ and C# I disagree around writing C/C++ in this way. (I am talking specifically about the side effect to 'index', not the use of a tertiary operator which is fine here)

I have seen far too many bugs creep in this way. I feel like C/C++ induce a desire to keep the code as short as possible and being 'clever'; even I often feel the need to do that in C++ when I am happy to write a more readable version in other programming languages.

The bugs are also hard to spot when skimming through the code: When there's a lot of code you will often miss the ++ on the 'index' as it's a long line compared to having '++index' on its own line.

Another good 'pet peeve' of mine is the following construct:

  for(int i = 10; i--;)
    // Do something until 'i' reaches 0

So many off-by-one errors...