#coding playgrounds

Someone was asking for tips on how to learn programming without having proper computer or laptop. That question was "How can I run Python scripts if I only have an Android tablet?"

We can go to a higher level of abstraction and answer "How can I run code in <x language> if I only have a smartphone or tablet?"

Coding Playgrounds

And the answer is coding playgrounds. They allow you to write and run code in a huge number of languages, straight from the mobile browser. My favorites are https://tio.run and https://replit.com/.

Specially Try It Online (tio.run), because it does not require any kind of login, works great from my phone, and supports and absurd amount of programming language (more than six hundred).

Replit is a more traditional environment, where you have an editor, a list of files, and even a built-in database to use. But requires a bigger screen, and it's a bit glitchy depending on the browser you're using.

Wikipedia has a list of tens of alternative code playgrounds to pick from, there's something for everyone's taste.

https://en.wikipedia.org/wiki/Comparison_of_online_source_code_playgrounds

Free Shells Online (Linux/FreeBSD/other Unix-like)

These one needs some extra steps, and for this reason I'd not suggest it for beginners. But on the other hand, you get a full Unix-like environment to work with, straight from your phone, tablet, or any device capable of using SSH.

But provided you can use SSH, there are lots of kind people offering free Linux/BSD shells on the Web. And with a free shell you'll get a compiler, bash, some megabytes of storage, an e-mail client, a database, etc. A fully functioning computer system.

Here's the free shell list: https://aruljohn.com/freeshell/

You'll need an SSH client, I use ConnectBot on Android: