Not very difficult. It's far harder to pull off the trick as the person typing in the question.

But you're in the wrong forum. It's definitely not C++. Go to "View Page Source" and you'll see that it's in Javascript and hence you'll see the full source code, or at least the full source code minus any imported scripts. It's been a while since I've played with Javascript, but since it's client-side, you can download the whole page and turn off your internet connection and successfully run it locally on your machine, so you have the full source code, so you can pick it apart. If you have questions, ask in the JavaScript section.

You could certainly also write this as a non-web-based application in C++.

It is possible to make an offline version of Peter Answers. I have done it, but I used Visual Basic not C++. I don't know anything about C++, but you can take a look at my program at: http://www.jonas-homepage.orgfree.com/jonas-answers.php. For the code you can e-mail me at <<snip>>