How to make a simple and appealing application in C# ?

Question

Hello, my name is Vladimir! I need some help with C#. I am studying computer engineering in Belgrade, Serbia, and I am 18 years old. C# is not really something I am good at, I am fairly new to it and I cannot grasp it at all, because until now I have been working only with C++ and C. I have an exam tomorrow in which I need to think of my own program / app and develop it on scene. I do not know what could I do and I don't have any clever ideas. I have searched through my notebooks trying to grasp C# but I cannot. For now, we have done some simple programs... For example:
1) In Forms, you have a text box, list box , group box and 5 radio buttons in the group box. The user makes an input number in the text box (exp. 126) and in then he checks off one of the radio buttons (exp. list all odd numbers from 1 to N) and then all the numbers need to be listed in the Listbox.
2) In Forms, you have 3 radio buttons which are in a separate panel from Forms. 1. Draw horizontal lines; 2. Draw vertical lines; 3. Draw vertical and horizontal lines

The user ticks off whichever radiobutton he wants, and then below that panel with the radiobuttons, the lines draw out automatically.

^These are only 2 of about 10 tasks we have done in school. (Just so you get the picture of the degree of our C# knowledge)

So please, I would really appreciate if somebody could show me how to make some interesting and simple program to fascinate my teacher.... And if there is anybody who can help, I would appreciate it even more if she / he could send me the entire code and the explanation for some more advanced parts of it.
Thanks in advance!