Try http://www.planetsourcecode.com and search for your code requirements, eg enter Calculator to the search criteria.
You should get numerous examples of what you want, which can be downloaded.

There doesn't seem to be an easy way of posting code up here,so any in depth stuff is going to take a heck of a lot of typing.

FYI

If you need code, start your project, get something happening in it, and then ask specific questions. You are more likely to get responses. Just a thought