CSCI 151 Lab 6: RPN Calculator

Overview

In this project, you will write a calculator that uses a stack and test it with JUnit.

Setup

Download the skeleton for this project.
Unpack the code into a new Eclipse Java project.

Description

We saw two implementations of the Stack interface. For this project, you will gain familiarity with the use of stack operations to implement a larger class. In particular, we will investigate how to create a mathematical calculator with a slightly different notation for operations.

An expression such as 2 + 3 * 5 is inherently ambiguous. To resolve it properly, we need to fix an order of operations, typically multiplication and division from left to right, then addition and subtraction. Alternatively, we can use parentheses to disambiguate. For example, (2 + 3) * 5 means to perform the addition first, whereas 2 + (3 * 5) means to perform the multiplication first.

Alternately, we can use postfix or Reverse Polish Notation to embed the precedence in the expression. By placing the operator at the end instead of in the middle of the two operands, we know exactly what operation to perform when. For example, the two example expressions above can be written as 2 3 5 * + (multiplication first) and 2 3 + 5 * (addition first).

This model of mathematical operators can be implemented with a stack. When the calculator sees an integer, it should be added to the stack. When it sees an operator (*, +, /, -, %), it should pop the two most recent elements from the stack, perform the operation, and then push the result back on the stack.

When the order of the operation matters, such as a - b, then your code should use the first element popped as b and the second element popped as a.

RPNCalc

In the rpn.model package, you will find the following classes:

`RPNCalc.java`

This is the main file you will have to complete. You will need to make a constructor, and complete the other indicated methods.

Step 1: Implement the four standard arithmetic operations together with mod (%). This should get your calculator to pass one basic test.
Step 2: Now implement the methods getLastValue, getNextToLastValue, numValuesLeft, and toString. This should get your calculator to pass several of the remaining tests.
Step 3: Now implement three additional operations:
- dup: When your calculator encounters the dup instruction, it should duplicate the top value on the stack.
- swap: When your calculator encounters the swap instruction, it should swap the top two values on the stack.
- pop: When your calculator encounters the pop instruction, it should pop the top value from the stack and discard it.
At this point your calculator should pass the remaining tests!

`RPNCalcTest.java`

These are the unit tests for your calculator. Your grade depends on passing these tests.

`Op.java`

This is an Enum. It is used in testing with JUnit, and you can safely ignore it.

What to Hand In

Submit your RPNCalc.java file along with any additional files you created.