C# (Windows Forms Application) Using While loop

Question

Hey guys. I started to study C# (Windows Forms Application) in Visual Studio 2010.
This is the Task I need to do but I have no idea how to do it. I have spent hours on this task but I failed at it. I looked on internet for help but I haven't found anything that would help me with the task, so if any of you could help me with this task I would really appreciate it. 
It really matters for me a lot because I did 2 star task easily but I want to submit every 3 star task.