Pytry / cli-rpn-calculator

This is a basic command line tool that implements (currently) four basic operators. Order of operations is not yet implemented, so at this point at most only 3 tokens can be entered and only in order (ie, two numbers separated by an operand). From the command prompt, simply enter "run" in the root directory of the project. Requires Java 8 to run.

#Postfix Calculator CLI

This is a simple Postfix expression based calculator API.

A postfix expression is an expression in which the operands are followed by the operator
unlike expressions in the familiar format, where the operator is in between the operands. For example, this standard "familiar" expression ...

6 * (5 - 2 + 4) 

... can be written in postfix form like this:

6 5 2 - 4 + *

Not every mathematical operator is implemented in this version at the moment.

To Run

Requires Java 8

On Linux

From the shell, execute the "run" script, using the current directory qualifier.

 $ ./run

Also make sure that permissions are correct, and that the "run" file is executable.

 $ chmod +x run

On Windows

Execute the "run.cmd" from a command prompt.

 > run

Structure

There are two modules (for now).

The "postfix-calculator" contains the core logic. Extraneous dependencies were avoided (such as importing an entire string utility or popular framework just to use one method).

The "cli" module is an implementation of a commandline tool where you can try out the various operations that have been implemented.

In the future, it would be great to add a RESTful service that provides an API for executing postfix command expressions. With that in mind, and to also allow for other methods of communication, I made sure that the core module could be used in any framework, while designing it in such a way as to be usable in a IoC container managed application (i.e. Spring). To verify this, I created the CLI using the Spring Boot framework.

If I were to spend more time on this, I would probably want to create a Spring Boot starter project that would automatically configure the application based on dependencies and classes that have been included in the classpath. The final application should end up as a single class with nothing more than the standard SpringBootApplication annotation.

Possible operators

ADDITION: +
SUBTRACTION: -
MULTIPLICATION: *
DIVISION: /

Examples:

Basic Syntax

> 1 1 +
2 +

Decimals Allowed

> 1.1 1     
0.1

Results Rounded

> 1.01 1.0 +
2 

Trailing '0' Decimal removed

> 1.0 1.0 + 
2 

Previous Values Persist

> 1.0 1.0 + 
2
> 3 -
-1 

Spaces are required

> -1
-1
> 2+22*
>Invalid Token

Operator only is allowed, and will calculate the last two numbers entered

> 1 1 +
1 +
> + 
2 +

Simple number entry will show the last number entered

> 1 2 3
3