Initially, when I was using a “dumbphone”, I learnt from websites online and tried out code using online compilers like http://ideone.com. It got annoying sometimes because I would finish typing a program (on a T9 keyboard! ) and then everything would disappear. Plus, it was really limited, because sandbox.
Later on, when I got a smartphone a year later, I switched to apps like AIDE (built my first Android app on my android phone ), Cppdroid, and C4droid.
Eventually, when I got a PC, and there was no power, or it had a fault, I would switch to mobile at times. I came to discover that, thanks to open-source, coding on mobile isn’t so… out there (I wouldn’t recommend it for newbies, though). In the past year, I’ve run Git, PHP, MySQL, Bootstrap, C++, Java, Android, Python, Octave/MATLAB and others on mobile. (Even saw an article about using Laravel and Composer on Android). Even now, when I need to make a quick fix, and I’m on the move, I just do it from my phone and git push.
Coding on mobile has its downsides. Very limited testability is one. Limited APIs available. Limited processing power. And autocorrect It can be useful, but it’s a pain. And only those who are really passionate about coding pull through.
That said, the sparkplug stuff is really awesome.