[axby]

Hi all, as a hobby I've been developing a scientific calculator with some neat features.

Available on:

* web (mobile or desktop): https://alexbarry.github.io/AlexCalc/

* Android: https://play.google.com/store/apps/details?id=net.alexbarry....

Some neat features:

* LaTeX equation display (I hated counting brackets on my old graphing calculators back in college, now I wouldn't have to if I wasn't ~10 years late in making this)

* variables (you can store variables with `1 + 2 -> x`, then access them `x^2 - 3`)

* unit operations, and unit conversions, e.g. `10 km / 2 minutes to mph`, or more fancily: `sqrt((3 kOhm + j*100 mH * 1000 kHz)/(1 S + j * 1 nF * 1000 kHz))`

* complex numbers (specifically focused on making it easy to enter complex numbers in polar form, in degrees, e.g. `5 angle 90`, but press the "degree" button)

* can enter input either via button presses or typing, so copying and pasting inputs works well

The core calculator parsing, evaluating, and LaTeX generation is in C++, with CMake build files. Using emscripten[0], this compiles to webassembly for the web version, and I can also compile this for Android and use JNI.

The library converting my generated LaTeX code to graphics is "MathJax"[1], a really nice browser library that I loved working with both in the web version and in the Android WebView.

I'm happy to receive any feedback at all. One big weakness currently are the syntax error messages, I haven't yet implemented a way to point to a particular position where an error occurs. If there is some nice parsing library that I could use instead, I might consider switching to that if it isn't too difficult. Currently the parsing uses a bunch of (fairly simple) regular expressions (e.g. check for number, check for optional unit, check for binary operator, add to stack, collapse stack. This ends up with a tree of nodes, and then this tree can either be evaluated or converted to LaTeX.)

I'm also interested in hearing any strategies for a decent cross platform UI. I didn't want to just include the HTML UI in a WebView on Android, since I figured it wouldn't be a great user experience. Originally I thought it would be small enough that I could just write two separate copies... but it turns out that there is a lot more UI code than I expected (automatically insert multiplication symbols on button presses, input history, storing "recently used units" when the button is pressed, etc...)

[0]: https://emscripten.org/

[1]: https://www.mathjax.org/

[zokier]

If you want to move beyond standard floats, this paper could be good starting point: https://dl.acm.org/doi/pdf/10.1145/3385412.3386037

Right now 0.1+0.2-0.3 results = 2.775557562 \cdot 10^{-17}, which depending on your viewpoint is either expected or unexpected. Also (0.1+0.2)-0.3 is simplified to 0.1+0.2-0.3 for display, but results a different value = 5.551115123 \cdot 10^{-17}

[axby]

Wow, thanks. This is way more complex than I expected. When I started working on this I thought that I might want to switch to "binary coded decimal"[0] to avoid issues with inputs like (0.1 + 0.2 - 0.3).

I haven't had a chance yet to read the full paper, but it talks about fixing trig issues too. Would this fix my (unfortunate) result for `e^(ipi) + 1` to be exactly 0, too (instead of something ugly like (-210^-16 + j1.22*10^-16)).

And is there an implementation I could use?

At some point I plan on open sourcing this code, so if I never manage to fix this then maybe someone else might someday do it. Originally I figured I could finish this whole project in a few months, especially after figuring out webassembly and discovering MathJax. But it ended up taking way longer than that, with little things constantly popping up that I wanted to fix before I could even think about sharing it.

[0]: https://en.wikipedia.org/wiki/Binary-coded_decimal

[enriquto]

Hey, it looks great, I love it!

Would it be feasible to support unicode variables? Having to spell the greek letters seems a bit clunky. If I type them directly it gives a parsing error. Notice that in modern LaTeX (say, xetex or luatex) you can do that. No need to type \'e to get é like we did in the nineties.

[axby]

Thanks a lot for trying it and the feedback!

Assuming C++ standard regex supports unicode, then this should be easy enough. I never thought to try this. I'll see if I can implement it later today or this weekend. Do you think the spelled out "alpha" should map to the same thing as "<unicode alpha character>"?

Also, do you mind if I ask how you are entering Greek letters directly? (e.g. are you a Greek speaker, using a Greek keyboard?) I'd like to better understand how people would like to use this. I'm happy to accommodate whatever I can, and I'm relying on people asking for it directly since I don't have any sort of tracking implemented. (The android version doesn't even request any INTERNET permission (or any permission).)