You won’t believe this but many corporations with Quantitative analytics libraries in Fixed Income are still written in C. Yes C and not C++ or other fancy computer languages. BNP Paribas, my previous employer is one of them.
Fully procedural and no concept encapsulation, not until you get to the application layer written by Computer Scientists. As a quantitive computer scientist I find it a shame that more of my piers cannot understand maths, and most mathematicians cannot see the benefits of object and functional languages.