In four years’ time, C will reach its 50th birthday, an anniversary also shared with PL/M and Prolog. Unlike those two, C remains immensely popular, it’s in the top ten of virtually every programming language popularity survey. Linux is mostly written in C. Python's CPython implementation, Perl, Matz's Ruby, about half of R, the MyISAM code for MySQL and even the first Java compiler were all written in C. The kernels of most operating systems (including Windows, Mac, Linux, iOS and Android) all feature C. Now we have a new C standard, C18, that was ratified a few months ago. A mere 198 Swiss Francs will buy the ISO/IEC 9899:2018 standard, all 520 pages of it; you can view the final draft of it for free, though, on openStd.org (PDF) to get a sense of the document. It's only really of use if you are a compiler writer who wants to be 100 percent conformant, or just curious. There's nothing new in C18, just more fixes, so it’s very much a continuation of C17. The last major changes to C were in C11, and those included variable length arrays, multi-threading support, better Unicode support, anonymous structures and unions, and a lot more.

C Holds Its Own Against C++

C++ has made some inroads into C's arena, especially since the C++ move semantics were added in C++11. When used in the right way, particularly with pointers to large objects, this results in better performance, fewer temporary copies, and lets C++ be used in places that were traditionally C territory (e.g., embedded). However, C++ compiled code is still generally a bit larger than that of C, because exception handling adds bulk and the number of inline template classes whose members get included. Out of curiosity, I compiled this in release mode in Visual C++ 2017:

#include 
int main()
{
    std::cout << "Hello world" << std::endl;
    return 0;
}

That compiled to a 10,752 bytes exe. The equivalent C program is:

#include 
int main()
{
    printf("hello world\n");
    return 0;
}

  That was 9,216 bytes long, or 85 percent of the size. Not a great deal of difference, but I could project this difference growing once you add in other classes. Code size is important because of the increasing number of Internet of Things (IoT) devices and the use of microcontrollers, which typically have RAM and ROM (Flash) measured in kilobytes. In the embedded field, C has actually gained market share between 2005 and 2018.

C is the Lingua Franca of Programming

C is the programming “common language.” Many programming-language compilers output C source code and let a C compiler do the heavy lifting of generating code (there are around 60 open-source compilers listed on this Github project page; there are also a few targeting C++, as well, but the C ones dominate). It's not difficult to understand, as C is the lowest-level portable language (the only one lower, assembly language, is tied to a CPU family).

Using C to Speed Up Languages

One of the most popular languages, standard Python, suffers from speed issues because of its interpreted code and use of dynamic variables. If you are doing numeric processing, then you'll be aware of the likes of NumPy, SciPy, and so on. NumPy is written in C. The standard implementation of Python is CPython, and so works well with libraries in C (and C++). An alternative way to speed up Python is by using one of the compilers such as Cython, PyPy, or Nuitka. Read about Python compilers speed tests.

C is Recognized as a Useful-to-Know Language

It’s probably not the first language any programmer wants to learn, but it appears to be popular as a second or third alternative. I’ve also seen it as a stepping-stone to learning C++, which is a superset of C. It's a matter of debate whether C++ is in decline, but C is by far the easier to learn of the two languages.

Conclusion

C has definitely earned its place as an infrastructure programming language. There is so much software out there that’s used every day, particularly on Linux, that C will be around for a very long time. Even though Go and Rust in particular are modern and better languages, C is so embedded in the infrastructure of the internet that I doubt it will ever be replaced. Over half of all active web servers are running Apache and Nginx, both written in C (according to Netcraft).It’s been around for almost 50 years, but C very much has a future.