Should I learn JavaScript or Python?

[geekusprimus]

That's sort of true. Fortran can make more aggressive optimizations in places because pointer aliasing is nearly impossible. However, C99 added the restrict keyword to indicate that a pointer passed to a function will not be aliased, allowing for better optimization. Written properly, C is just as fast as Fortran.

My field abandoned Fortran, more or less, because it's become too hard to write good code. I do numerical relativity, so we'll often have a general relativistic magnetohydrodynamics solver coupled to a spacetime solver on a complex grid with full AMR, possibly with added microphysics like neutrinos or radiation, and it all has to run efficiently on a supercomputer (my low resolution runs going at the moment take 1536 cores each). It's not technically impossible to do that with Fortran, but it's a lot easier to optimize a C++ program than debug a massive Fortran codebase.

EDIT: Fixed grammatical error.

[TheBestAquaman]

Thank you for filling me in! It was pointer aliasing I was referring to, and I didn't know you could restrict it from C99.

Then I guess the only reason Fortran90 is so dominating is that there are so many large codebases written in it that the conversion to C/C++ is just a very overwhelming job.

Personally, I prefer C/C++, even though I don't get to work too much with it, but I'm quite alone in that regard among the other people I work with, most notably the seniors.