If you going to reivent the wheel, at least show your attempts.
Please note, that it is not a homework site. We won't do your homework for you. However we are always willing to help solve problems you encountered, correct mistakes you made in your code and answer your questions.
We didn't see your attemts to solve this youself and so we cannot correct mistakes you didn't made and answer questions you didn't ask. To get help you should do something yourself and get real problems with something. If your problem is "I don't understand a thing", then you should go back to basics and study again. As it is impossible to find deriviative of function without knowledge in ariphmetics, you cannot do more complex tasks in programming without clear understanding of basics