lab03 - Fun with shapes: Pointers and Structs

Collaboration policy

This lab must be completed individually

Goals of this lab

The goal of this lab is to demonstrate how we can abstract “things” in the world (such as geometric objects) into program contructs. We also hope that you will get a lot more practice with using pointers, passing pointers to functions and using pointers along with structs. Y

You will continue to use the test-driven development (TDD) process to develop high quality and well-tested code in a systematic manner. When you run into problems with your code, remember to use the skills we have been learning such as code tracing and drawing pointer diagrams, to understand the dynamics of your program and how it is interacting with memory.

Step by Step Instructions

Step 1: Getting Ready

1. Go to github and find a repo for lab03 assigned to your GitHub id.

2. Log on to your CSIL account.

3. Change into your ~/cs16 directory

4. Clone your empty lab03 repo into your ~/cs16 directory.

5. In your empty repo, do git checkout -b main to establish that you are on the main branch as your default branch.

Step 2: Obtain the starter code

The starter code is in this repo:

• https://github.com/ucsb-cs16-w23/STARTER-lab03

The URL for cloning this repo is this: git@github.com:ucsb-cs16-w23/STARTER-lab03.git

Previous labs contain instruction for the process of:

• Adding a starter remote for this repo
• Pulling the code from that starter remote into your own repo.

Please do those steps now, and then do a git push origin main to populate your own repo with the starter code.

If you need help with these steps:

• First consult previous labs for more detailed instructions.
• Then, if you are still having trouble, ask the staff for help during discussion section or office hours.

Once you’ve populated your repo, typing the ls command should show you the following files in your current directory

$ ls
Makefile			pointsApproxEqualTest.cpp
README.md			shapeFuncs.cpp
areaOfBoxTest.cpp		shapeFuncs.h
boxesApproxEqualTest.cpp	shapes.h
distanceBetweenTest.cpp		tddFuncs.cpp
initBoxTest.cpp			tddFuncs.h
initPointTest.cpp		utility.cpp
pointToStringTest.cpp		utility.h
$ 

Step 3: Reviewing the files and what your tasks are

Here is a brief description of each of the files and expected implementation.

Note that some of the files are organized in pairs of matching .h/.cpp files:

• These include:
  • shapeFuncs.h/shapeFuncs.cpp
  • tddFuncs.h/tddFuncs.cpp
  • utililty.h/utility.cpp
• In these cases, the .h file has function declarations (also known as function prototypes) and the .cpp file has the function definitions.
• Knowing about this separation is important. Look over the contents of some of the .h files and .cpp files that are in pairs like this.
• Be sure, for future exams/homework, that you can identify whether some arbitrary C++ code looks more like it would appear in a .h or a .cpp file.
• Also be sure that you know how to spot the difference between function declarations (aka prototypes), and function definitions.

The shapes.h file is different; it isn’t paired with any .cpp file. That’s because it contains struct declarations used in the other files.

Finally, there are also a variety of .cpp files that have the suffix Test in their names. Each of these contains a main function, and code that runs our tests. These are the same tests that run on Gradescope.

Here’s an overview of all of the files and their purpose:

• utility.h/cpp : Implement any of your own functions that you will need to solve the problems in this lab
• tddFuncs.h/cpp : Functions that you may use to test your code
• shapes.h : Contains the declaration of two structs: Point and Box. These data structures will be used in other files e.g. shapeFuncs.h/cpp
• shapeFuncs.h/cpp : Functions to compute metrics on geometric constructs such as points and boxes (see shapes.h)
• *Test.cpp: Each of the files that end in Test.cpp contain code to test a particular function in shapeFuncs.cpp.

Here are some further notes about the files that end in Test.cpp:

• As an example, distanceBetweenTest.cpp contains test code to test your implementation of the distanceBetween() function in shapeFuncs.cpp.
• Note that each *Test.cpp file tests contains a main function, which means that each test file along with its dependent code is meant to be compiled into a separate executable.
• The provided Makefile makes sure that this is in fact the case.

The rationale behind this approach is that each function in shapeFuncs.cpp can be developed and tested independently as much as possible.

Tasks for this lab

Here is a list of your tasks for this lab. You will see that we are working on one function at a time, seeing the tests fail, then editing code to see the tests pass.

(1) Get distanceBetween working

• Run make and see the given code being compiled.
• Run ./distanceBetweenTest and see it fail.
• Edit the distanceBetween function in shapeFuncs.cpp to replace with correct code.
• Run ./distanceBetweenTest and see it pass.
• Commit and push your code to github with commands:
  • git status to see which files have been changed and need to be added.
  • Repeat git add filename for each filename that you have changed
  • For example: git add shapeFuncs.cpp
  • git commit -m "distanceBetween function is now passing tests" (the exact comment is up to you; this is a suggestion)
  • git push origin main
• You should now be able to make a submission to Gradescope and see that you are getting at least partial credit for the lab (i.e. some of your tests are working.)

  (2) Understand the pointsApproxEqual function

• Run ./pointsApproxEqualTest and see it pass.
• Look at the code in pointsApproxEqualTest.cpp and shapeFuncs.cpp and understand how it works.
• Notice how the pointsApproxEqual() function uses the distanceBetween() function that you just wrote and tested, rather than writing new code within pointsApproxEqual() that repeats the logic of distanceBetween().
• The takeaway here is that you want to keep your code as DRY as possible (DRY==Don’t Repeat Yourself).
• You also want to only reuse code that has already been tested.
• You’ll need to understand pointsApproxEqual() to get ./boxesApproxEqual to pass.

There is no code to commit for this step; this is just a step for you to read some code and understand it.

(3) Get initPoint working

• Run ./initPointTest and see it fail.
• Looking at the test code in initPointTest.cpp, figure out what the initPoint function is supposed to do.
• Edit the initPoint function in shapeFuncs.cpp to replace the stub with correct code.
• Run ./initPointTest and see it pass.
• Commit and push your code to github with commands:
  • git status to see which files have been changed and need to be added.
  • For each file that has changed, use: git add filename (replacing filename as needed)
  • git commit -m "distanceBetween function is now passing tests" (the exact comment is up to you; this is a suggestion)
  • git push origin main
• Make a submission on Gradescope from your GitHub repo and see if your grade is going up.

(4) Understand your code by drawing a picture

Now, as preparation for homework and exam questions, reason about why your code works.

• Do this by drawing a pointer diagram that shows the state of memory right before the initPoint function returns when it is called for the very first time by the test code.
• Your pointer diagram should show the value of member variables x and y of the struct object p1 in initPointTest.cpp as well as the relationship between p1 and the formal parameter p of the function initPoint.
• You should also show the formal parameters xVal and yVal in memory and indicate whether or not they are colocated in memory with any other variables (such as x and y).
• This drawing is only for your own purposes; we are not grading it. However, you are encouraged to make the drawing on a piece of paper and show it to one of the staff during lab section or office hours to get feedback on whether your understanding is correct.

(5) Get boxesApproxEqual working

• Run ./boxesApproxEqualTest and see it fail.
• Edit the boxesApproxEqual function in shapeFuncs.cpp to replace the stub with correct code. As you do, consider adding an approxEqual function that takes two double values into utility.h and utility.cpp, as this will make your coding job easier, and keep you code “DRYer”.
• Also, consider reusing the pointsApproxEqual function in your boxesApproxEqual solution. Remember that the && operator is the symbol for “logical and” in C++.
• Run ./boxesApproxEqualTest and see it pass.
• Reason about why your code worked, draw a diagram to show the relationship between the formal and actual parameters. You don’t need to submit the diagram but you may be asked to draw such a diagram on an exam!
• Commit and push your changes to GitHub (by now, you should know the appropriate commands).
• Make a submission on Gradescope from your GitHub repo and see if your grade is going up.

(5) Get initBox working

• Run ./initBoxTest and see it fail
• Edit the initBox function in shapeFuncs.cpp to replace with correct code. As you do, remember that you use -> to access members of a struct through a pointer, but simply . to access members of a struct directly. You may need both in your answer.
• Run ./initBoxTest and see it pass
• Commit and push your code to GitHub, and try submitting to Gradescope.

(6) Get areaOfBox working

• Run ./areaOfBoxTest and see it fail
• Edit the areaOfBox function in shapeFuncs.cpp to replace with correct code.
• Run ./areaOfBoxTest and see it pass
• Commit and push your code to GitHub, and try submitting to Gradescope.

(7) Get boxToString tests set up

• Run ./pointToStringTest and see it pass; we’ll use that as a basis to develop boxToString.
• Copy pointToStringTest.cpp to boxToStringTest.cpp (the Unix command is cp) and write code for tests for the boxToString function.
  • Look in shapeFuncs.cpp at the boxToString function stub for an example of the format you need for boxToString’s return values.
  • Make tests for different precisions, just like pointToString has.
• Add code to the Makefile so that boxToString runs. Just follow the model—adding code in the Makefile for boxToStringTest everywhere you see code for pointToStringTest
• Run make
• Commit and push your code to github including all of the files you have changed.
• Try another Gradescope submission

(8) Get boxToString working

• Run ./boxToStringTest and see the tests fail
• Fix the definition of boxToString in shapeFuncs.cpp
• See the test ./boxToStringTest pass
• Commit and push your code to github including all of the files you have changed.
• Try another Gradescope submission

Even if you now got 100 on Gradescope, please now check your work before submitting.

Step 4: Checking your work before submitting

When you are finished, you should be able to type make clean and then make tests and see the following output:

-bash-4.2$ make clean
/bin/rm -f distanceBetweenTest initPointTest pointsApproxEqualTest boxesApproxEqualTest initBoxTest areaOfBoxTest pointToStringTest *.o
-bash-4.2$ make tests
g++ -Wall -Wno-uninitialized   -c -o distanceBetweenTest.o distanceBetweenTest.cpp
g++ -Wall -Wno-uninitialized   -c -o tddFuncs.o tddFuncs.cpp
g++ -Wall -Wno-uninitialized   -c -o utility.o utility.cpp
g++ -Wall -Wno-uninitialized   -c -o shapeFuncs.o shapeFuncs.cpp
g++ -Wall -Wno-uninitialized  distanceBetweenTest.o tddFuncs.o utility.o shapeFuncs.o -o distanceBetweenTest
g++ -Wall -Wno-uninitialized   -c -o initPointTest.o initPointTest.cpp
g++ -Wall -Wno-uninitialized  initPointTest.o tddFuncs.o utility.o shapeFuncs.o -o initPointTest
g++ -Wall -Wno-uninitialized   -c -o pointsApproxEqualTest.o pointsApproxEqualTest.cpp
g++ -Wall -Wno-uninitialized  pointsApproxEqualTest.o tddFuncs.o utility.o shapeFuncs.o -o pointsApproxEqualTest
g++ -Wall -Wno-uninitialized   -c -o boxesApproxEqualTest.o boxesApproxEqualTest.cpp
g++ -Wall -Wno-uninitialized  boxesApproxEqualTest.o tddFuncs.o utility.o shapeFuncs.o -o boxesApproxEqualTest
g++ -Wall -Wno-uninitialized   -c -o initBoxTest.o initBoxTest.cpp
g++ -Wall -Wno-uninitialized  initBoxTest.o tddFuncs.o utility.o shapeFuncs.o -o initBoxTest
g++ -Wall -Wno-uninitialized   -c -o areaOfBoxTest.o areaOfBoxTest.cpp
g++ -Wall -Wno-uninitialized  areaOfBoxTest.o tddFuncs.o utility.o shapeFuncs.o -o areaOfBoxTest
g++ -Wall -Wno-uninitialized   -c -o pointToStringTest.o pointToStringTest.cpp
g++ -Wall -Wno-uninitialized  pointToStringTest.o tddFuncs.o utility.o shapeFuncs.o -o pointToStringTest
./distanceBetweenTest
PASSED: distanceBetween(p1,p2)
PASSED: distanceBetween(p2,p1)
PASSED: distanceBetween(p3,p4)
PASSED: distanceBetween(p4,p5)
PASSED: distanceBetween(p5,p3)
./initPointTest
PASSED: pointsApproxEqual(p1,p1Expected)
PASSED: pointsApproxEqual(p2,p2Expected)
PASSED: pointsApproxEqual(p3,p3Expected)
PASSED: pointsApproxEqual(p4,p4Expected)
./pointsApproxEqualTest
PASSED: pointsApproxEqual(p1,p1)
PASSED: pointsApproxEqual(p1,p2)
PASSED: assertFalse(pointsApproxEqual(p2,p1)
./boxesApproxEqualTest
PASSED: boxesApproxEqual(b0,b0)
PASSED: boxesApproxEqual(b1,b0)
PASSED: boxesApproxEqual(b0,b1)
PASSED: boxesApproxEqual(b0,b2)
PASSED: boxesApproxEqual(b0,b3)
PASSED: boxesApproxEqual(b0,b4)
PASSED: boxesApproxEqual(b5,b6)
PASSED: boxesApproxEqual(b6,b5)
./initBoxTest
PASSED: boxesApproxEqual(b1,b1Expected)
PASSED: boxesApproxEqual(b2,b2Expected)
PASSED: boxesApproxEqual(b1,b2)
./areaOfBoxTest
PASSED: areaOfBox(r)
PASSED: areaOfBox(s)
PASSED: areaOfBox(t)
PASSED: areaOfBox(u)
./pointToStringTest
PASSED: pointToString(p1)
PASSED: pointToString(p2)
PASSED: pointToString(p2,1)
PASSED: pointToString(p2,4)
PASSED: pointToString(p2,5)
-bash-4.2$

Plus, some output at the end with the output of your boxToStringTest

./boxToStringTest
PASSED: boxToString(b1,1)
PASSED: boxToString(b1,2)
PASSED: boxToString(b1,3)
PASSED: boxToString(b1,4)
PASSED: boxToString(b1,5)
PASSED: boxToString(b1,6)
-bash-4.2$

At that point, if you haven’t already, submit on Gradescope

Step 5: Checking your code style

Please check that you have followed these style guidelines:

1. Indentation is neat, consistent and follows good practice (see below)
2. Variable name choice: variables should have sensible names. More on indentation: Your code should be indented neatly. Code that is inside braces should be indented, and code that is at the same “level” of nesting inside braces should be indented in a consistent way. Follow the examples from lecture, the sample code, and from the textbook.

Your submission should be on-time. If you miss the deadline, you are subject to getting a zero. The instructor may or may not extend the deadline for late submissions at their discretion.