enable syntax highlighting in C/C++ examples

[Rastaban]

Enable syntax highlighting by adding cpp where it was missing from the markdown code block. I also cleaned up some of the whitespace and comments where lines didn't line up right or felt a little off.

I also added a C++17 example fix to one of the docs.

[jborsecnik]

@mikeblome, does this need to go to the private repo?

@Rastaban, Microsoft authors and contributors are asked to make content contributions through the private repository so the content can be staged and validated by the current validation rules. For more information, see Should I work in a private or a public repo?

If you need help getting set up to work in the private repo, see Fork and clone a reposistory.

Also, you should link your Microsoft and GitHub aliases. See Set up Git repository locally for documentation to link your GitHub alias with your Microsoft account.

[mikeblome]

Phil is not a regular contributor or core PM, so I think we can merge this PR in the public repo base on this rule : "Microsoft employees from other teams can work in public repos at this time to ensure their contributions are reviewed by the article author. For example, if you work in CSS and only contribute occasionally, working in the public repository is lighter and easier for most docs contributions."

[jborsecnik]

@mikeblome, okay. Can you sign off on this PR? Thanks.