When you use ticket machines to buy a train ticket, they will find the shortest route for you.
This is done thanks to a very complicated program which computes the shortest path between two points.
In my case, I was working for the Italian national railways company. The program doing the above calculations used bit fields. These are uncommon structures used to pack information densely.
These structures are so uncommon that even compilers find it hard to compile them.
I evaluated these compilers: CPP Builder, Watcom C++, IBM VisualAge for C++, Borland C++, Symantec C++.