I am forced to learn and practice C#, is there any applications that support and can be used to write programs in C#?
Yes you can use mono
For a nice IDE to work in try monodevelop
This will also pull in all the necessary runtimes needed.
What you are looking for is Mono, which is, quoting from the project's website:
Mono also comes with an Integrated Development Environment (IDE): MonoDevelop. Both softwares are packaged for Ubuntu.
This last package depends on the first one. Installing this package will automatically install the other.