RPN.md

Context

An RPN calculator computes expressions written in Reverse Polish Notation.

An RPN expression or postfix expression is one of the following :

• a number X, in wich case the value of the expression is that of X,
• a sequence of form E1 E2 OP where E1 and E2 are RPN expressions and OP is an arithmetic operation.

Samples :

20 5 /        => 20/5 = 4
4 2 + 3 -     => (4+2)-3 = 3
3 5 8 * 7 + * => 3*((5*8)+7) = 141
7 2 - 3 4     => 5 3 4

Objective

Write a program that take an expression (e.g. "20 5 /") and prints the result (e.g. "4")

The following operators should be supported: +, -, /, *

1. program can optionally support floating point number
2. program can optionally support negative number

Options

• Add the SQRT operator:

    9 SQRT      => √9 = 3

• Add the SWAP operator:

    1 2 3 SWAP  => 1 3 2

• Add the DUP operator:

    2 4 DUP     => 2 4 4

• Add the MAX operator:

    5 3 4 2 9 1 MAX   => MAX(5, 3, 4, 2, 9, 1) = 9
    4 5 MAX 1 2 MAX * => MAX(4,5) * MAX(1,2) = 10