Remember that calculator lab we did? From Unit 2? Yeah, that one. Well, we're going to refactor it, and add some functionality to it.
Modify your calculator program so it checks that any text boxes contain numeric values and warn the user if it doesn't. Also, add in absolute value, square root, and sign functions; these should only use the number in the first text box. Finally, you should add a small, labelled TextBox that is for the number of places after the decimal point to round to.
HINTS: This one should be fairly simple. If you have any problems, ask.
As always, design a useful and proper interface. Make sure you use good software engineering practices, like keeping your code DRY and avoiding lines of code that don't do anything useful.