Is there any BigDecimal class for C? - c

I looked all over the internet and I can't seem to find one.
There is something similar in Java, but I need to use C (preferably something I can use locally). Has anyone got any ideas?

Copy of my answer:
If you need to do operations with HUGE decimal values I would suggest you to use http://gmplib.org/ library. I've used it a lot with C and C++.

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Solving a Variable Equation defined by the User

Answers in C, Python, C++ or Javascript would be very much appreciated.
I've read a few books, done all the examples. Now I'd like to write a simple program.
But, I already ran into the following roadblock:
My intention is to take an equation from the user and save it in a variable,
For example:
-3*X+4 or pow(2,(sin(cos(x))/5)) > [In valid C Math syntax]
And then calculate the given expression for a certain X-Value.
Something like this:
printf("%g", UserFunction(3.2)) // Input 3.2 for X in User's Function and Print Result
Any ideas? For the life of me, I can't figure this out. Adding to my frustration, the solution is likely a very simply one. Thank you in advance.
There isn't a simple way to do this in C but I think muParser may be useful to you, it is written in C++ but has C binding. ExprTk is also an option but looks like it is C++ only, on the plus side it looks much easier to get interesting results with.
Another option may be the Expression Evaluation which is part of Libav. It is in C and the eval.h header has some good descriptions of the interface.
In compiled languages like C, C++, or Java there is no easy way to do this--you basically have to rewrite a whole compiler (or use an external library with an interpreter). This is only trivial in "scripting" languages like Python and Javascript, which have a function (often called "eval()") that evaluates expressions at runtime. This function is often dangerous, because it can also do things like call functions with side effects.
Ffmpeg/libav has a nice simple function evaluator you could use.

library for integer arrays in C

Maybe it's a dumb question but:
I'm looking for a library for the classic functions on arrays of Integers (sorting, searching ...) in C, does anyone know a good one ?
I could rewrite those functions but, to be honest, I'm quite lazy.
More generally, is there a list of known libraries somewhere?
Thanks in advance

is it possible to use Eigen with c?

I don't know very much about template programming, and I currently use gsl. I'm interested in seeing if Eigen can be use in C. Has anybody used Eigen in C before? Is there something I can test to find out if it will be easy?
Since Eigen is a C++ template library, it cannot be directly used with C.
Hypothetically, one could wrap the C++ templates into a C API, and use that. However, that's bound to involve a lot of work and would strike me as a bit pointless (one might as well use existing C libraries for linear algebra).
AFAIK, Eigen is a template-only library. C doesn't support templates. So without writing a bunch of wrapper functions that expose a C-style interface, no.

Where can I find a good guide to writing C Collections?

I remember having read a very good guide to writing collections. By that I mean, it described using macros to generate types with type parameters, kind of like C++ templates. I'm not sure if it was written by Rusty Russell, but it was someone I recognized. It was posted on hackernews or proggit... I wanted to write a new C library and has searched google for the past 30 min for this guide to no avail. Anybody remember?
This guide fits your description:
Collections in C by Armin Ronacher.
One example would be queue(3), see queue.h.

Is there a way to translate C code to Ruby?

I'm sitting with massive amounts of legacy C code that needs to be converted to Ruby for a project.
I've seen Ruby to C translators online, but not the other way around. Would there be a simple way to approach this particular problem?
You'll either have to write a C to Ruby translator, which is possible but the effort might not be justifiable, or you could split the C code up into smaller modules that you can create Ruby wrappers for as a first step. Once they're all wrapped in Ruby and the main control flow is done in Ruby, you can write a test harness (both to verify correctness of your replacement code and to aid reverse engineering) and start replacing the C modules with Ruby modules.
The divide & conquer approach should work with regular Ruby if you use the modules as native extensions but obviously this will cause further problems if you're targeting something like JRuby as your runtime environment. If you want to do something similar in JRuby as per your comment, you're looking at wrapping the C modules in JNI and calling through from the JVM that way. Either way will allow your C code to interact with the Ruby code, but the two approaches are not interchangeable.
Neither approach is going to be quick and both are going to be a lot of work.
You could:
Write a C interpreter in Ruby (very hard).
Wrap the compiled C code with something like SWIG (much easier).
Programming in C and programming in Ruby bear completely different programming paradigms. So while the old saying that you can write Fortran (or C in this case) code in any language is true, the Ruby code that you would eventually get by machine translation wouldn't be Ruby at all, except syntactically.
So, IMHO, any way other than manual (and done by proficient Rubyists, I might add) would be either impossible, or at least not useful at all.
Maybe you can try this https://github.com/jackieju/CPP2Ruby/
It's fresh for cpp but existed longer for c to ruby
You can try Abap2Ruby. It can also convert cpp to ruby.

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