reverse-polish-calculator

An interactive reverse polish calculator. This tiny project is an extension of the example given in chapter 4 of the book "The C Programming Language" second edition, by Brian W. Kernighan and Dennis M. Ritchie (ISBN: 978-93-325-4944-9). Basically exersice 4.3 t0 4.9.

Compilation

The Makefile here is taken from simple-make-build. To build this project just call make, the makefile handles the rest.

# clone repo
git clone --depth=1 https://github.com/SidhBhat/reverse-polish-calculator
# build
make
# and execute...
./build/reverse-polish-calculator

Syntax

The moment you run the progran you are presented with a interactive prompt, where you can type your calculations. The expressions you type here are in the reverse polish syntax.

Every expression consists a function and it's arguments in order to the left of the function. the function can return only one value, which is the value of the expression. Suppose the function is func with arguments a, b and c, we would write:

a b c func

we can pass this value to a another function func2 with two arguments as:

arg1 a b c func func 2

Here we notice a b c func is bahaving as a single agrument to func2.

Thus $a + (b - c)$ would become a b c - + and $(a + b) - c$ will be a b + c -. Let us take a more complicated expression $sin^2(a) + cos^4(b)$ we would espress it as a sin 2 ^ b cos ^ 4 +. Let us see one more example $e^x cos(2x + 3) + ln(y)$:

2 x * 3 + cos e x ^ * y ln +

The reverse polish syntax is easy to implement in code as it is independant of operator precedance, but is pretty unintutive to the human reader.

Supported Functions

sin
cos
tan
sinh
cosh
tanh
pow
ln
log
sqrt
cbrt

Supported binary operators

+
-
*
/
%
^

Commands

These are commands that take zero arguments but allow one to modify the program environment:

# Get the last answer
ans
# clear the stack memory
clear
# exit the program
exit

Some special operators

? Operator returns the value of the last calculation, so for example 2 3 * ? + would be equal to $2 \times 3$ added to itself and would produce $12$.

= The assignment operator assigns a variable to the value of the second argument. A variable must be the first argument. If that is not the case an error is thrown. The value of the expression is equal to the assignment value that is, the second argument. We can use this fact to perform assignments (multiple in a single expression) along with computations.

a 1 sin 2 ^ = b 1 cos 2 ^ = +

would evalute to $1$ as well as assign $a = sin^2 (1)$ and $b = cos^2 (1)$. Thus if we run a b + now we would again get $1$, which is cool.

Variables

We have 26 variables which can hold values. These are the english small alphabets. We can assign values to these variables using the = operator.

Develpoment Branch

The branch beta is used for devlopment purposes. When you build here the program prints the stack along with the answer. This is used for debugging purpose. If you use this branch please make sure to remove the relevant lines when merging into main.

Contributing

As with my other projects you can start contributing by simply creating a pull request. And for suggesions you can contact me by email¹.

Footnotes

1. available on my profile ↩