If you want help with your homework, please edit your question to show what you've come up with so far, and explain why it isn't working the way you expected it to. See also How do I ask and answer homework questions? and Open letter to students with homework problems — Klaus Gütter 41 secs ago

Note that Stack Overflow is better suited to specific questions about narrow, well-defined errors; we tend to turn away questions that regard working code. Questions about good design practices are more welcome on our sister site Software Engineering. — Charles Duffy 48 secs ago