Structural engineers, and many other engineers for that matter, extensively use software to carry out complex numerical computations. While most of them use such software, a few will end up developing such software for others to use. Today, there is a plethora of programming languages available and the free and open source software movement ahs made available compilers that are free.
Here is my take on some of the programming languages that I have used for numerical computations at different points of time:
Pascal, Turbo Pascal to be precise
Java