C/C++ and C# compiler

To install C/C++ compiler type the following in terminal(to open terminal go to Application-->accessories-->Terminal):

sudo apt-get install build-essential

If you want integated development environment for any language type this:

sudo apt-get install (compiler name here)

Eg. For geany(C/C++ lightweight compiler)
sudo apt-get install geany

I personally like geany because it gives me the look and feel of dev-Cpp another C/C++ compiler for windows.

YES THERE ARE c# COMPILERS IN LINX!!!!!!!!!!!!!!!!!!!!!!!!!
The magic is done by mono compiler

Install mono in ubuntu just by typing
sudo apt-get install mono

or
search install using synaptic.

Find more about MONO here.

You can develop even .NET applications in linux using MONO.
You can install MONO in windows , MACOSX,etc etc i.e. its cross platform.
Download MONO