A simple calculator

I designed a homework for HTML/CSS/JS basics. Implement a web-based calculator! It's quite simple to write a program for an experienced programmer, but for a beginner it may take a while.


Also, there are some rules:

  1. all buttons are functional as a real calculator does
  2. single page, no links to external resources such as jQuery
  3. multi-browser supported is prefered.
  4. as precise as it looks

Do you wanna try? I have writen a version (tested in Chrome)