# Reverse Polish notation calculator — manual

This is a manual for my Reverse Polish notation calculator tool, since a lot of people were confused.

## Description

**Reverse Polish notation** (RPN) or **postfix notation** is a way to write mathematical expressions. Unlike **infix notation**, which is probably what you're familiar with, operators are written *after* the numbers, not *in between*. For instance, if you want to write the sum of `3`

and `4`

, you'd do it like this in **infix**:

3 + 4

Whereas in **postfix**:
3 4 +

That's the basics of it, but it's somewhat more complicated than that (try to write `5/(3+4)`

). Don't worry though, it's pretty easy.
You've got a stack of number blocks. You can only grab books from and push books to the top of the stack. Currently, it has no blocks, but let's give it some. For example, let's add `5`

, `3`

and `4`

.

5...
[ 5 ]
3...
[ 3 ]
[ 5 ]
4!
[ 4 ]
[ 3 ]
[ 5 ]

You've also got some magic spells you can use to apply operations to number blocks.
Let's do addition.
[ 4 ]->|+++|
[ 3 ]->|+++|->[ 7 ]
[ 5 ] [ 5 ]