I just found a nifty web site/application for those who do mobile development - or just think about coding problems while running around town.
The folks at ideone.com have a pretty spiffy programmers tool - at least for small programs. It will compile (if needed) and execute a source text - possibly with standard input. They even have an API so "native" applications running on various devices can use this service - and the applications seem to exist. I've used the android one, which is ugly but functional.
There are limits on memory, time and processes, and you can't do any network programming. Except for that last bit, nothing that's really a problem for the trivial types of things this interface is suited for.
What it is good for - at least if you don't have the language on your mobile device, which lack some manufacturers seem to see as a good thing - is a quick check on an idea that you would otherwise have to write a note about, and would probably bug you (or at least they bug me) until you got someplace to check them out.
Now that fossil scm has been ported to Android, and a language interface that stores program files as text on the sdcard, you can even put a real development model in place.