1) You're going to need more info to get #1 answered. When do you get that error? How are you invoking it?
2) Input fields in web pages are typically in a form. The form is POSTed back to the server when the user submits the form. The form value can be read through the Request.Form[] collection or through model binding in ASP.NET MVC. You only need to browse this site to find countless examples of saving data to a database. Another good resource would be to Bing "ScottGu"
3) Use a free JavaScript library to do this. Try
this one[
^].
FYI, all compilers in the .NET Framework are accessible via the command line.
Cheers.