Lab 4: Selection sort

Due: 4/26 11:59pm

1. Goals

By the time you have finished this lab, you should have demonstrated your ability to code a selection sort on a an array of pointers to objects in C++. You will also get more practice with doing test-driven development of object-oriented C++ code.

2. Getting Started

This lab may be done solo, or in pairs.

Before you begin working on the lab, please decide if you will work solo or with a partner. If you decide to work with a partner, read the Working in pairs section of the course webpage.

Once you and your partner are in agreement, choose an initial driver and navigator, and have the driver log into their account.

3. Copying some programs from my directory

Visit the following web link:

You should see a listing of several C++ programs. We are going to copy those into your ~~/{{site.course | downcase}}/{{page.num}} directory all at once with the following command:

cp ~emre/public_html/cs32/code/lab4/* ~/cs32/lab4

The * symbol in this command is a "wildcard"–it means that we want all of the files from the source directory copy be copied into the destination directory namely ~/cs32/lab4.

After doing this command, if you cd into ~/cs32/lab4, and use the ls command, you should see several files in the directory–the same ones that you see if you visit the link above.

If so, you are ready to move on to the next step.

If you don't see those files, go back through the instructions and make sure you didn't miss a step. If you still have trouble, ask your TA for assistance.

4. Understanding the Starting Point Code

4.1. Understanding the tddFuncs.cpp code

You may find it interesting to compare the versions of tddFuncs.h and tddFuncs.cpp from lab 2 with the ones from this lab.

You do NOT need to make any changes to these files. However, they serve the purpose of showing how we can use template functions in C++ and Template Specialization to create code that is more "DRY", i.e. follows the adage "Don't Repeat Yourself".

Here are links to the versions of these files from lab 2 and this week:

lab2 lab4

Some things to notice:

  • In the lab2 version of tddFuncs.cpp, there was duplicated code–identical versions of assertEquals for both int and std::string. In the lab4 version, this has been DRY'ed up and factored out into a template in the lab4 tddFuncs.h.
  • In the lab4 version of tddFuncs.cpp, there are also two overloaded versions of the function assertEquals that are NOT using the template. These versions of the function are needed because C-strings (i.e. const char * and const char * const values) cannot be compared with the == operator. The version for two C-strings used strcmp instead, while the version for a C-string and an std::string simply converts the C-string to a C++ string and invokes the template version for std::string.

Again, you don't need to do anything with this for this lab, so if you want to gloss over this for now and come back to it later, that's fine. You need to look it over though, and understand what is going on.

A final note: the way we overloaded the functions here does work, and it has the advantage of being easy to understand and follow. However, it is probably not the "current best practice" way of handing this, and strictly speaking, is not "template specialization", it is rather just "garden variety overloading". We'll go over the "better way", i.e. true template specialization, in a future lab or lecture (although each variant has its uses). For now, if you are curious, and want to "read ahead", consider the following StackOverflow link:

4.2. Understanding the CXXFLAGS in the Makefile

In this week's Makefile, as with last weeks, we have the following.

CXXFLAGS = -Wall -Wextra -Wno-unused-parameter -Wno-unused-private-field

# Change to this before final submission:
# CXXFLAGS = -Wall -Wextra -Werror

See the explanation in lab 2 of these two definitons for CXXFLAGS. It will be important for you to modify these before submitting to make sure that your code will compile with those flags set.

4.3. Understanding the Student and Roster classes

The Student.h and Student.cpp classes are mostly unchanged from lab 2, except for the addition of a few new methods.

Please look those over–these are mostly methods for reading in a Student from a comma-separated string, and are there so that we can read in students from a CSV file (i.e. a file of comma separated values) into a Roster.

The Roster.h and Roster.cpp files, though, are new.

You'll see that the Roster.h file contains the specification of a class that represents a collection of Students. It represents this collection with a simple fixed size C++ array of pointers to Student objects. THERE ARE CERTAINLY BETTER WAYS TO IMPLEMENT A COLLECTION OF STUDENTS. The point for this week's lab, though, is to understand sorting algorithms.

We will implement a selection sort on the array of pointers to Student objects. Since we only have to swap the pointers in the array–we don't have to swap the entire Student object–our algorithm will run in the same amount of time no matter how large the actual Student objects may be. In general, this is a good idea if/when one is working with large objects.

The files where you will be making changes this week are:

  • Student.cpp, where you'll be updating the methods that you wrote in lab 2. Don't just copy over the entire file though, because if you do, you'll lose the new methods that we supplied you with in the starting point code.
  • Roster.cpp, where you'll be replacing stubs with correct code.

4.4. Understanding the tests: testStudent.cpp and tddFuncs.cpp

What you should do next is to look through the test cases in testStudent.cpp (which includes all the tests from the three test files in lab 2) and testRoster1.cpp, testRoster2.cpp and testRoster3.cpp

Look over these files and understand how they work. Then, type make tests to compile and run all of the tests.

You can also type, for example, make testRoster1 and ./testRoster1 to make and run these tests one at a time.

5. Make all the test cases pass

When you are ready, start editing Student.cpp, replacing the stubs for the constructor first, and then each of the stubs for the other functions. Get all the tests in testStudent to pass first.

Then, read through testRoster1.cpp and see what methods in Roster.cpp you think you need to update in order to get those tests to pass.

Then proceed to do the same with testRoster2.cpp and testRoster3.cpp.

6. Checking your work before submitting

When you are finished, you should be able to type make clean and then make tests and see that all the test cases pass.

At that point, you are ready to try submitting to the Gradescope system.

7. Submitting via Gradescope

The lab assignment "Lab 4" should appear in your Gradescope dashboard in CMPSC 32. If you haven't submitted anything for this assignment yet, Gradescope will prompt you to upload your files.

For this lab, you will need to upload your modified files (i.e. Student.cpp and Roster.cpp). The autograder will ignore other files, so do not modify them if you want to observe the same behavior as what is run on Gradescope. For this lab, you are required to submit your files with your github repo.

If you already submitted something on Gradescope, it will take you to their "Autograder Results" page. There is a "Resubmit" button on the bottom right that will allow you to update the files for your submission.

For this lab, if everything is correct, you'll see a successful submission passing all of the autograder tests.

Remember to add your partner to Groups Members for this submission on Gradescope if applicable. At this point, if you worked in a pair, it is a good idea for both partners to log into Gradescope and check if you can see the uploaded files for Lab4.

Author: Mehmet Emre


The material for this class is based on Prof. Richert Wang's material for CS 32