# CSE 373, Winter 2019: Homework 2: Extra credit

## Summary

Due Friday February 1 at 11:59pm

This document contains a list of some recommended extra credit. Before you start working on extra credit, you should probably look at the course policies on extra credit.

For any extra credit you implement, you should include in your group writeup:

1. A description of what you implemented
2. Instructions on how exactly to use the new commands you added (as well as example inputs for your grader to try)
3. A description of anything else you want the grader to look at or be aware of

## Ideas

Here are some suggested extra credit ideas. Feel free to also come up with your own extra credit ideas if you don't feel like doing these ones -- the only restriction is that your idea needs to related to the course content and needs be approved by the course instructor first.

1. Implement a solve function

Try writing a solve(...) function that solves for some user-specified variable. For example, solve(equal(3, x + 2), x) would return 1.

Before implementing this, you will need to add support for the equal(x, y) math operator. (Here, we treat equal(x, y) as having the same meaning as $x = y$.)

You can add support for this equals operator similarly to how you added support for operators like + or *. You will also need to add a handleSolve(...) method to ExpressionManipulator and register your handleSolve(...) method inside the Calculator class's constructor.

What exactly your solve function does is up to you: you either try and approximate an answer perhaps within a user-specified range (easier) or try and solve the equation symbolically (harder).

2. Implement a derive function

Try implementing a function that can take the derivative of some user-specified expression. Your derive function doesn't need to support arbitrary expressions: you could have it support only polynomials, for example. (If you support more types of expressions, that'll be more extra credit).

3. Implement more plotting functions or a drawing library

Currently, we can only plot line plots. Try adding more plotting functions to draw different kinds of charts and visualizations!

You should add a new method to the ImageDrawer class for each new plotting function you implement. Please do not change or modify any of the existing methods.

Alternatively, add commands that can let the user draw arbitrary images. Our graphing calculator, under the hood, is built on top of a Graphics object (which is the same one you used in CSE 142 or 143 to draw images). The ImageDrawer class has a method you can call to gain access to the Graphics object.

For bonus points, draw an image using those commands and include the image (and the commands used to draw the image) in your group writeup.

4. Implement control flow (if statements, loops) and implement a programming language

We will first start by implementing two basic control flow primitives: if statements, and loops.

Try creating an if(cond, then, else) function. The function should first evaluate the cond expression and returns then if it evaluates to true and returns else otherwise.

Since our expressions always evaluate to numbers, we'll treat 1 as being synonymous to true, and 0 as being synonymous to 'false'.

Similarly, implement a repeat(amount, body) function that repeatedly evalutes the body multiple times.

(See ControlFlowManipulators for some starter code.)

Once you have finished implementing those two primitives, add more and more control flow elements (while loops, user-defined functions, etc...) to let the user compute increasingly more complex things.