Lab 1: Gitting Started with C++

A Git repository is a directory containing files that are managed by Git. This looks just like a normal directory under most circumstances, but it contains a hidden .git subdirectory (that you generally shouldn’t touch). By using the git command inside of a repository, you can manage the files in that directory.

Git is a distributed version control system: there can be multiple different copies of the same repository on different computers, some of which might contain different information than others. When developing software, we occasionally use the git tool to move information from one copy of a repository to another. Two operations you’ll be performing in this lab are cloning (which creates a copy of a repository) and pushing (which sends your changes back to the original repository).

GitHub is a popular website that stores and manages Git repositories. Software developers can keep their repository on GitHub and then copy content to and from it from their own computers. We will not be using that website, although we will be using something very similar. Instead, we will use Swarthmore’s own GitHub site at https://github.swarthmore.edu.

In order to start using the Swarthmore GitHub website, you should follow the one-time setup instructions on Dr. Tia Newhall’s webpage. Note that these are one-time instructions; if you have already followed them for a different course (such as CS31), you don’t need to do so again.

For the labs in this course, you will be using repositories that we have already created; this is similar to how students use the update21 script in CS21 to fetch the initial files for a given assignment. That repository — the directory of files we have created for you — exists on the Swarthmore GitHub site. To edit those files, you will have to clone the repository into your home directory on the CS lab machines. You can make the clone by running this command:

Make sure to replace <your-username> with your Swarthmore username. For instance, you might write

if your Swarthmore username were zpalmer2. (It isn’t.)

Running the clone command will cause git to create a directory named e.g. lab01-zpalmer2 in your current directory. You should cd into that directory now.

Your newly-cloned repository contains several files; we will edit one named Questions.txt now. Use your favorite editor to open Questions.txt and answer the questions it contains.

Once you are finished, run git status. You should see something like this:

This indicates that changes have been made to the file named Questions.txt but that Git has not yet been told about those changes. In order to record the changes that we have made, we must commit them. Run the following commands:

You should now see something like this:

This indicates that Questions.txt has now been "staged"; that is, it will be part of the next set of changes we create. In a more complicated scenario, we might want to run git add several times or do something else more complicated to create a single "change". We use git add to add the changes for certain files to the staging area in order to create a new version of our directory.

In this case, the only file we’re changing is Questions.txt, so we’re ready to create our change. Run the following command:

This command will create and record the change. It will attach the comment (here, "Answered the questions.") to the new versions of our files. If we run git status now, we see something like this:

The message "working directory clean" indicates that our Git repository knows about all of the changes that we’ve made. You can even look at the history of the changes you have made by running git log. (If you do, you can exit the log viewer by pressing q.)

Remember: your directory on the CS network is only a copy of the "real" repository stored on the Swarthmore GitHub site! At this point, your copied repository is aware of your new changes, but the Swarthmore GitHub version is not. We can see this because the previous git status message included "Your branch is ahead of 'origin/master' by 1 commit.", which tells us that we have a commit that the GitHub does not. To send the commit that we have made to the Swarthmore GitHub, we can run git push.

Now, git status looks like this:

The git push command attempts to send every new commit we have made back to the original place from which we cloned our repository.

To be certain that the Swarthmore GitHub website has your changes, visit your repository on that webpage. The URL will be https://github.swarthmore.edu/cs35-f19/lab01-<your-username> (again replacing <your-username> appropriately). If everything worked out, you should be able to view the GitHub copy of Questions.txt by clicking on the like-named link on that page. Make sure that the contents of that file match what you expect.

In order to use Git to update your lab repository, you should perform the following steps:

Your task is to create a program which performs the following tasks:

The files you will read all have the same form. The first number appearing in the file indicates how many numbers the file contains. The rest of the numbers in the file are the numbers to summarize. For instance, if a file contains

then the sequence we want to read contains the four numbers 5, 0, 8, and 3. You are guaranteed that all of the numbers in the file are non-negative; you are also guaranteed that there are at least two numbers.

Once you have read all of the numbers in the file, you should print the following summaries:

You are required to write at least three functions other than main to complete this task. Those functions should not print any values; they should return information for main to print.

You should compile your program using the following command:

Then, you can run your program with this command:

Here are two example runs of the above program:

Your output doesn’t have to look exactly like this, but it should produce the same results.

It’s always good to plan out what you intend to write before you write it. What functions will you need? How will you read and store your data?

In this assignment, we have the following suggestions:

Once you are finished writing the above programs, remember to commit and push them! You can double-check your submission by looking at the GitHub website. We will grade what is shown there by the due date.