How much time do you want to spend doing this?
I did a calculator program back in the 1980's.
Standard coding methods on cpu's are not accurate enough.
Floating point errors multiply especially when doing recursion like calculating the tides for best time to plan a fishing holiday.
Don't think because you have a 32bit cpu, 32 or 64bit floating point is accurate.
I wrote it using BCD, Binary Code Decimals on a 6805.
Did the maths the same way they teach at school, carry the 1 etc.
Calculators only need to be 4bit cpu's because you only use the numbers 0-9.
It is more tricky when you get to sin/cos stuff but lookups tables help.
But you probably won't need that as the Pi ARM cpu is much faster than a 4MHz 6805.
Plotting is different as you don't need so much accuracy.
It would make an interesting project for Ultibo, there is a graphing unit in this example.
https://github.com/ultibohub/Examples/t ... c3000/RPi2
Ultibo can have multiple console windows, one can be used for GUI buttons, one for plotting and another for the digit display.
Done some of my own plotting stuff and it turned out to be easier than I thought
https://ultibo.org/forum/viewtopic.php? ... tting#p792
The 7" Pi display works fine and touch works.
https://ultibo.org/forum/viewtopic.php? ... t=plotting
It looks like DPI displays might have a chance of working too.
No one has tested this with Ultibo yet
https://learn.adafruit.com/adafruit-dpi ... ah-ttl-tft
DPI uses most/nearly all the GPIO.
Smaller SPI display also work.
Using Ultibo also gets you 2 second boots.
The GUI stuff is early days, but drawing blocks is easy and pik33 has even used DMA which makes it fast.
Fonts are easy with a font tool in the github.
If you want to make a portable battery powered calc then an eInk display with a Zero?
Anyone make ~5" touch mono eInk display?
You could start with Processing 3.0 on PC and port to Pi, but Processing uses Java and only runs at a decent speed on a Pi 3
Oh, and Processing can port to Android.
You can use Python and pygame and gnuplot.py
Netbeans on PC then port to Pi, also Java but uses JavaFX for display speed and you don't need a X window.
Many, many more ways to do it.
Ascii plot in terminal screen?
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges