define function -> "def f(x,y,z)=x^2*y+z"
define varialbe -> "x=PI/2"
basic algebra -> "f(4)*3^7"
comparison -> "1==sin(PI/2)"
if you want a calulator that doesn't crahs all the time, stay away! There a millions of better calulators than this. I have also somewhat remade this project in Rust. Still nothing i'd use but you can take a look at it Here!