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If you clink the link it should take you to an example program with that exact code. You can compile and run it and get the output. ideone is just an online compiler + environment where you can compile and run code in various languages. The URL spelled out is http://ideone.com/klyfLl

I guess seeing is believing. It really does work. To make things easy for you, here it is in action.

To elaborate, just with "official" tools you have:

On Windows you have PowerShell installed by default since Win7 and JScript/VBScript since Win98. With .NET framework you also get C# and VB.Net compilers. As free downloads, you have C/C++ compiler as a part of Windows SDK and all of above in Visual Studio Express.

On Linux, in all main stream distros you get at least one of Perl/Python, often - GCC and sometimes Ruby, not to mention Bash and Awk. Repositories have a ton of other compilers and libraries with bindings available on your fingertips.

And even though I'm not familiar with OSX, I do know that Xcode is just a download away.

And then you have browsers, with things like http://jsfiddle.net/ , http://ideone.com/ , http://repl.it/ or http://scratch.mit.edu/projects/editor/

And then you have all the other languages and IDEs, free and proprietary all over the web...

If anything, we have overabundance of languages, but lack of interest due to all the content to consume chipping away the need to create.

I was waiting for such a course with our API in the backend and here it is :)

You could give http://ideone.com/ a try.

Here is a brief explanation:
What is ideone?
Ideone is something more than a pastebin; it's an online compiler and debugging tool which allows to compile and run code online in more than 40 programming languages.

I don't know how much debugging type stuff you want to do, but you might enjoy using a web-based IDE like IDE One. You can use any language you want, and if I were you, I'd type my code in a text editor that allows for syntax highlighting, like Notepad++, which can be run without an install.

http://ideone.com/

Cloned your code and added a classical fourth-order Runge Kutta. Here. There isn't really any difference, presumably because you used 100 000 time steps. The difference between Euler and RK4 is tiny for non-stiff problems and small time steps.

So I guess either your interpretation is wrong, or he is wrong.

Doing a reply-to-self because I checked my interpretation using a numerical simulation. I wrote some python 3 code, which does a reasonably realistic simulation of a baseball being hit for a home run. Slashdot's lameness filter wouldn't let me post it, so I put it here: http://ideone.com/yeP4y

The results:

u= 36.86184199300463 v= 25.810939635797073 Ray= 0.07075915491208162 KE+PE+heat= 147.825
u= 30.646253624059415 v= 12.467830176777555 Ray= 0.07075939744839914 KE+PE+heat= 147.82340481003814
u= 26.608846983666997 v= 1.6625489055858707 Ray= 0.07075957710355621 KE+PE+heat= 147.8224303518585
u= 23.559420165753 v= -7.761841618975968 Ray= 0.08597247439794412 KE+PE+heat= 147.82171310054588
u= 20.86163826256129 v= -16.094802395195508 Ray= 0.10413207421166563 KE+PE+heat= 147.82115230900214
range= 120.88936569485678 , vs 194.17117929504738 from theory without air resistance
u= 18.25141606403427 v= -23.242506129076933 Ray= 0.12066666645699123 KE+PE+heat= 147.8207286473949
u= 15.70673363979356 v= -29.088976584679852 Ray= 0.1353850869274781 KE+PE+heat= 147.8204307883206
u= 13.30143766684643 v= -33.65200048062784 Ray= 0.14867603720136566 KE+PE+heat= 147.8202356199746
u= 11.11267911406159 v= -37.07517115834146 Ray= 0.16096016949002218 KE+PE+heat= 147.8201144079141
u= 9.186200956690504 v= -39.564763699985484 Ray= 0.17255826567110216 KE+PE+heat= 147.82004160975018

The notation is that u and v are the x and y components of the velocity vector, "Ray" is the expression that Ray seems to be claiming is a constant of the motion, and the final column is the total energy, which should be conserved.

I tested my code two ways: (1) Energy is very nearly conserved. (2) If I turn off air friction, the range is very nearly as calculated by theory.

Let R be the expression that Ray says is a constant, under my interpretation of his variables. Then dR/dt appears to be very nearly zero early on in the simulation. However, later on it starts to drift upward. So I suspect that one of the following is true: (1) Ray is wrong; (2) my interpretation of his notation is wrong; or (3) my simulation doesn't use good enough numerical techniques to demonstrate with good precision that Ray is right.

Anyone who's got Runge-Kutta, etc., on the tip of their tongue want to try a better simulation of this?

...try IdeOne. Code doesn't run in the browser -- it's compiled and runs server-side -- but it supports dozens of languages, including esoteric ones like intercal and whitespace, and allows you to optionally publish your code snippets, a la pastebin.

-a.d.-

I haven't checked yet, but I'm sure someone out there is making an IDE / compiler based on html5 so we can drop what ever IDE application we use for it.

I'm not sure if this is what you meant, but here's some IDE's:
http://coderun.com/
http://shiftedit.net/
http://compilr.com/
http://ideone.com/
http://py-ide-online.appspot.com/

Go play with Python on...

http://ideone.com/

"Ideone is something more than a pastebin; it's an online compiler and debugging tool which allows
to compile and run code online in more than 40 programming languages."

Have a book...
http://www.swaroopch.com/notes/Python

Have two...
http://www.greenteapress.com/thinkpython/thinkpython.html

Have a link to the Python Learning Foundation site...
http://www.awaretek.com/plf.html

Whether you choose python or something else, you could start fiddling around here before going through the hassle of installing a development environment.