Your question isn't urgent to anyone else so don't put that in your question, it is more a put off that makes people think you haven't left enough time to solve your problem. I don't see why this can be urgent as if you don't have an Development Environment (which is what you're looking for) how can oyu know how to program anything useful in C#????
Anyway, in answer to your question, it depends what OS your running and how much you want to pay. If your running Mac, forget it, C# is a Microsoft thing. If your running Windows, the best you can get is Microsoft Visual Studio, but unless your a student, you ain't gonna get it free. Try searching Google for: "C# Development Environment" plus 'Windows' or 'Linux' depending on which you are running, e.g.:
http://www.google.co.uk/search?sourceid=chrome&ie=UTF-8&q=c%23+development+environment+linux[
^] I have used in the past Linux, though Microsoft VS is far better :)
Hope this helps,
Ed :)
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