Postfix-calculator

A simple caclulator that evaluates postfix expressions (to learn about Queues, Stacks, and Exception handling).

How to use the calculator?

If you clone this repository, then in the Postfix-calculator directory run (in Windows)

java main\TestCalc.java

(If it runs successfully) You will see the prompt:

Enter the post-fix expression:

Your input should have each symbol separated by a space.

Eg:

Enter the post-fix expression: 2 3 +

The result: 5.0

Enter the post-fix expression: 

You will be prompted for another expression. And it will continue until you type "done" (case insensitive).

Enter the post-fix expression: done

Operators supported: +, -, *, /, ^

Logic:

• The calculator's evaluation logic is implemented in the evaluate() method of PfCalculator.java:
  • Input: A Queue.
  • Method:
    • Remove each element from the input queue one at a time and push it to a Stack.
    • If the element is recognized as an operator, pop 2 string values off of the stack, convert them to their numeric equivalents, perform the calculation with those values, and push the result (as a string) back onto the stack.
    • Otherwise, simply push the token onto the stack. When the input queue is empty, then pop the stack for the result.
  • Output: The result of the expression.