C hasn't decreased in popularity, but there are some indications that C++ has been losing popularity in the last ten years (e.g. tiobe).

With GoLang and Rust coming on tap for real, the next ten years will be very interesting as far as C++ goes (they really have the potential of "eating" C++ more than C in my opinion).

If you look at this site:

http://langpop.com/

And turn off everything (set to 0) except Github, it is rather interesting seeing what new code is being produced today. So while I definitely think the legacy C++ code base is massive, and that jobs will exist for some time to come (40+ years), it doesn't seem like a lot of new projects are choosing C++ (I certainly wouldn't for a new project, unless it was a game, or I needed a specific library written in C++).

Security issues are a major boat anchor around C++'s neck, and while the newer standards solve a lot of those issues, if you're going to have to almost completely re-write to that, you could equally consider Rust or GoLang when they've stabilized a little.

But, right now in 2015, C++ is fine and the jobs should exist enough for it to be worthwhile. I am more just saying "keep an eye on it."

I think C++ will always be a big player. I'm sure it will lose popularity to some new languages as time goes on but I doubt it will go away completely. There's just too much stuff already written in it and too many companies dependent.