Calculator

This project is an example implementation of a simple CLI calculator. It is meant to be part of a tutoring project where a learner develops a calculator in increasing levels of complexity.

Starting off

• V1: a CLI app that asks for two numbers and prints their sum.
  • Keep in mind how you can test your code from the start. Write unit tests.
  • How do you handle invalid input?
  • Try to keep track of your code in Git and keep a clean history.
  • Play around with various methods of reading input and writing output. E.g., System.in/System.out but also System.console. The former can be interacted with in various ways too (InputStream, Reader, etc.).
• V2: a CLI app that asks for one input, parsing e.g. 2+4 and printing the result. Start with only supporting non-negative integers and summation.
  • Keep those unit tests in mind! Does your program also understand 2 + 4?
  • Start with a single addition, then work towards implementing multiple additions such as 1 + 2 + 3 + 4.

Ramping up difficulty

• V3: add subtraction to your V2 calculator. How much code do you need to change?
  • This might also be a good time to implement negative integers.
  • Does your code understand 1 + -2? Should it?
  • Does your code understand -4 -1? Should it?
• V4: add multiplication to your V3 calculator. Be mindful of order of operations! How much code do you need to change?
  • Check that 3 + 2 * 5 = 13, not 25.
  • Does your code understand -3 * -4 = 12 too?
• V5: add division to your V4 calculator. How much code do you need to change?
  • Initially you can have your calculator print 8 / 3 = 3, but it might be nice to have it print something resembling 2.66667.
• V6: add rational numbers to your V5 calculator. How much code do you need to change?
  • Now your calculator should be able to compute that 0.5 * 4 = 2.

Getting into a pickle

• V7: add brackets to your V6 calculator. How much code do you need to change?
  • Now your calculator should be able to compute that (1 + 2) * 3 = 9 (and not 7).

Advanced challenges

• V8: add implicit multiplication to your V7 calculator. That is, parse 2(3) as if it said 2*(3) and solve to 6.
  • This is tricky to get right, so no worries if this takes a while or if you do not want to finish this version, or if you do not get all corner cases to behave as you would like.
  • Think of cases like (1)(2)(3) and also 1(2)3(4(5)).
  • You can take a peek at the CalculatorTest file in this repository to find more edge cases.
• V9: add exponentiation to your V8 (or V7 if you skipped V8) calculator. You can use for example ** or ^ as an operator; using two characters might be more challenging, depending on how you implemented your calculator so far.
  • Think of order of operations.
• V10: add root extraction to your V9 calculator. You can use full on root as an operator or the Unicode character √ (or both, if you want, like this example implementation). It can work as 2√4 = 2 and 3√27 = 3, so that it is still a binary operator.
  • Bonus points if you implement a unary square root operator (let's call that sqrt).

Repository contents

This repository will contain an example implementation of a V10 calculator with unary operator support. Furthermore, it will contain all other versions described above in earlier commits. To make this more clear, every commit that makes the implementation reach the next version is tagged. This makes it easy to browse an example implementation for every version, especially in GitHub.

This particular commit contains a V3 implementation.

Contributing

This repository is by no means perfect, so contributions are welcome. Feel free to open a merge request for relatively small changes. Please open an issue to discuss before you engage in large refactoring or adding large features.