HelloWorld

Welcome to CS 102 on GitHub! Here, you will find code repositories for all lectures, labs and programming assignments.

This is our obligatory Hello World public repository. If you only see this repository under the CS 102 GitHub Organization Account This means that you are yet to be designated as a member of this organization. This process starts by you. All you need to do is provide your GitHub account username to your TA/CP and you will be added within the first week of classes.

In this course, we will using the following VirtualBox Appliance as the reference system for grading:

http://ee-classes.usc.edu/cs101/cs102-vm.ova

This is an Ubuntu 12.04 LTS VM. You can login using:

• Username: cs102
• Password: memory

Lab 01 – Exercises

Git Setup

You need to setup git on every machine you plan to use for CS 102 this semester. This includes your own desktop/laptop(s) and the course VM. The VM has git already installed. You do, however, still need to configure it.

Download & Install Git

Start by downloading the latest git package from the official git website:

http://git-scm.com/downloads

Installing the downloaded package should be straight forward.

If you are using aludra.usc.edu, run the following set of commands to install git on your account:

cp ~/.cshrc ~/.cshrc.backup
echo "" >> ~/.cshrc
echo "# Git Setup" >> ~/.cshrc
echo "source /usr/usc/git/default/setup.csh" >> ~/.cshrc
source ~/.cshrc

To your installtion on aludra or any other system, run the following command in the terminal (use Git Bash in Windows and make sure you open a new terminal window in Mac):

git --version

which should give you the current version of git installed on your system.

Configure Git

In this stage you tell git what your name and email are and your editor of choice. In Linux or MacOS, you should run the following commands in the terminal. In Windows, you need use the Git Bash application.

#Set your name and email
git config --global user.name "Tommy Trojan"
git config --global user.email "ttrojan@usc.edu"

#Pick your editor of choice to edit commit messages (not code)
# Note that you should pick an editor that is installed on your machine
git config --global core.editor emacs

#Lets get pretty colored output!
git config --global color.ui auto

Due to different operating systems treating the end of line ('\n') character differently, you can make git normalize the line feed for you based on your OS:

• Linux & MacOS

#LF Normalization (Linux & MacOS)
git config --global core.autocrlf input

• Windows

#LF Normalization (Windows)
git config --global core.autocrlf true

SSH Key-based Authentication

By default, git communicates with servers using the git protocol that works over SSH. Therefore, it is advised to generate SSH keys for authentication purposes.

This guide will walk you through generating an SSH keypair. You need to follow Steps 1 and 3 only. Step 2 is only needed if you have keys already generated. This page auto-detects your operating system, so make sure your are following the correct instructions. Keep in mind that step 2 is only needed if you have an existing key pair:

https://help.github.com/articles/generating-ssh-keys

You will need the contents of the id_rsa.pub in the following part of the assignment.

Demo

Show your TA/CP the output of the following commands:

#List local git configuration options
git config --list

and

#Show the contents of the default SSH public key
cat ~/.ssh/id_rsa.pub

GitHub Account

As discussed in the presentation, git is a distributed version control system. We will be using git extensively this semester in labs and in programming assignments. GitHub is a development ecosystem based around git. In CS 102, we will be using GitHub to host our git repositories and we will take advantage of other GitHub features such as the issue tracker and wiki.

Creating Your Account

If you already have a GitHub account and you wish to use it for this course, you can skip to following section.

We start by visiting GitHub's sign-up page. You are free to choose your username and email. It does not necessarily need to match your USCNet account. Your email, however, needs the email you used in your git configuration.

https://github.com/signup/free

You will be sent an email to verify your email address. Do that before proceeding.

Update Your Profile

You need to update your profile to include your name and SSH public key. There are also some optional settings you can change such as your avatar (profile picture) and email notifications.

In your Profile Settings:

• Put your real name in the name field. This is to ensure the TAs & CPs know who you are regardless of your username.
• [Optional] Change your avatar

In your SSH Key Settings:

• Click on Add SSH Key
• Provide a name for the key, such as "CS102 VM Key"
• Copy the contents of your id_rsa.pub file and paste them into the key field
• Click Add Key

[Optional] You can add more emails to your GitHub account using the Email Settings page.

[Optional] Set your notification preferences on the Notification Settings page.

Demo

1. Show your TA/CP your GitHub Contributions page at https://github.com/username where username is your GitHub username.
2. Show your TA/CP your SSH Key settings page.

HelloWorld Repository

The most basic use of git is to checkout a code repository to your local machine. That is called cloning a repository. To clone this repository, you run the following command:

cd
git clone git@github.com:usc-csci102-spring2013/HelloWorld.git
cd HelloWorld

This will create a copy of the HelloWorld repository on your machine in a directory named HelloWorld. Unlike other version control systems such as subversion, you now have a complete copy of the whole repository including its history.

Basic Operations

To make sure your repository is up to date with the version on the server, you pull the most recent changes to your local copy:

git pull

If you want to check the commit history of this repository, you just type:

git log

This lists the commit history in reverse chronological order. You navigate this screen using the SPACE, ENTER or arrow keys. To quit press q.

You can check the history of a specific file using git log:

git log HelloWorld.cpp

You can do the same on GitHub by clicking the HelloWorld.cpp file and pressing the History button

FightOn Repsitory

Now, lets create our own repositry and using git to keep track of our code. Create a public repository called FightOn using GitHub:

https://github.com/new

• Add a optional description
• This should be a public respository
• Initialize this repository with a README
• Do not add a .gitignore file.

Make sure you are not inside the HelloWorld repository on your local machine:

cd
pwd

Then, clone the repository to your own machine using the SSH-based URL, i.e. the one starting with git@github.com/....

Create a C++ file called FightOn.cpp using your editor of choice, e.g. emacs, vi or gedit.

• Write a HelloWorld-style program the prints Fight On!.
• Compile your code using the g++ compiler: g++ FightOn.cpp
• Run it to make sure it works

Now, that you have a fully functioning program, you should add it to your repository and push it to GitHub. To find out the current state of your repository, you check its status:

git status

This will show that you have two untracked files: FightOn.cpp and a.out. Since it is bad practice to push binary files to your repository, we are only going to add the FightOn program:

git add FightOn.cpp

Now, check the status and try to read through the whole message and see if it makes sense:

git status

At this stage, your FightOn.cpp file is added and ready to be committed. When you commit a file or a collection of files you are recording the changes to the repository:

git commit -m "Created the FightOn HelloWorld-like application"

The text after the -m is actually a mandatory message that git adds as part of the commit. If you don't supply a message via the commandline, an editor will automatically open prompting you enter a message.

If you refresh your FightOn repository webpage on GitHub, you will notice that it does not yet have your FightOn.cpp. The reason being that although you committed the file locally, you have yet to push the changes to the server. You do that by:

git push

Finally, lets do a git status again. You will notice that a.out is still listed as an untracked file. To ignore unwanted files such as log files or executables, we create a special file called .gitignore (note the leading dot) and we list all the unwanted files (one per line).

So, create a .gitignore file and list the a.out file in it then do a git status! Don't forget to push your .gitignore to your repository.

Demo

1. Show your TA/CP your FightOn repository on GitHub which should include:
   • FightOn.cpp
   • .gitignore
2. Go to the GitHub Account Registration form:
   • Fill the form
   • Show your TA/CP the confirmation page.

Git Reources

For more information about git, visit our Git Resources document.