C was born in 1972 (that's over 45 years ago!) and C++ was born in 1985. You might think that after so long time they would have stopped being relevant (I mean you don’t see a lot of T-Fords driving around) - but you'd be wrong, and here are a few reasons why:

1) They represent the hardware in a reasonable way

Both C and C++ let you have (more or less) full control of the hardware, and there are still many applications where this is vital.

A few of the benefits with hardware control are:

Better usage of resources

Deterministic usage of resources

Advanced memory manipulation and control

This can be done in other languages as well, but C and C++ do this in a very elegant manner.

2) You can write very efficient code

Yes, a skilled developer can write very efficient code in languages like C# or Java but I argue that it’s easier done in C or C++.

3) They are portable

There are languages that are more suitable for platform independent development, but the fact is that multi-platform applications can be efficiently written in C and C++.

4) They evolve

Today’s C and C++ have evolved quite a bit since their birth and they continue to do so (even if C++ currently evolves at a higher pace than C does). And it's not only the syntax that evolves - IDEs, code analyzers, refactoring tools, build systems - the whole ecosystems continues to get better and better.

5) They are widely used

A lot of software has been written in C and C++ that many of us use daily, for example:

OSes: Windows, MacOSX, iOS, Linux, Android

Databases: MariaDB/MySQL, PostgreSQL, Oracle, SQL Server

Productivity tools: Microsoft Office, LibreOffice, Visual Studio

Now this doesn't mean that C and C++ will exist forever, but they will at least exist and be relevant as long as these projects do (and I can assure you that they will be around for a long time). Basically a lot of code exists that has been written in C and C++ and that code is too valuable to / will take very long time to replace.

Finally, I should mention that both C and C++ have gotten a lot of competition lately (e.g. golang) that are gaining traction that will sometimes replace C / C++ in newly written applications. But C and C++ will continue to be used for a long time, and I wouldn't be surprised if C and C++ are still around in 45 years from now.