1.2.1. Long-term storage on the hard drive

1. Files and Folders
   

   Our computers organize things into Files and Folders. Folders (aka "directories") represent locations. Folders can contain other folders ("subfolders") or files. Files are all the rest - our text files, images, music, videos, and so on. The actual data the computer stores, that we can read and write.

   Folders and files both have names, but files often also have extensions. This is the information after the "." that specifies what kind of file it is:

   File name	File type
   readme.txt	Plain-text file
   photo10.jpg	jpeg photo/image file
   song.mp3	mp3 audio file
   video.mp4	mp4 video file
   homework.docx	Microsoft Word file
   unit01.zip	Compressed (zipped) file

   In Windows it often turns off extensions by default. I would recommend turning on extensions to make differentiating your course project files more easy. Check the Reference portion of the textbook for steps (search for "Turning on viewing file extensions in Windows").

2. Paths
   

   Each Operating System might store their filesystems differently, but a lot of the concepts are the same. A filesystem is conceptually based on paper folders (like in a file cabinet) where you have a lot of folders labeled, and each folder can contain multiple files. If we didn't come up with some way to organize the data on our computers it would be difficult to find everything in the jumbled mess.

   Our system has some sort of root directory (or folder), like the roots of a tree - the starting point. In Windows, it's often your C:\ drive. In Linux and Mac, it's usually just labeled /. Often there are system folders in the root directory, and then we have some kind of "home" or "my documents" folder set aside for us to store our files in.

   In a path, each folder is separated by a slash - in Windows, it's backslash (\) and in Mac and Linux it's forwardslash (/).

   • Windows user directory: C:\Users\USERNAME\Documents
   • Linux/Mac user directory: /home/USERNAME/Documents

   As we navigate a filesystem, going into a subfolder will build up the directory path you're currently in. There is an "up" button on most filesystem explorers as well, where the "up" command takes you out of your current folder and back into its parent folder.

   1. Absolute paths and relative paths
      

      When we type out a full path, such as

      C:\Users\Singh\Homework\CS200\Project1.cpp

      this is known as an absolute path. It gives the full path from the base C:\ drive to the file in question.

      While we're working within our programs, we can also use relative paths to locate nearby files. Let's say we are working with Project1.cpp inside the CS200 folder. That folder also contains a hello.txt file. In order to have Project1.cpp open hello.txt, we just use "hello.txt".

      If hello.txt were inside a subfolder like "data/", then Project1.cpp would have to access it with "data/hello.txt". If hello.txt were one directory UP, then Project1.cpp would have to access it with "../hello.txt". The "../" goes up (or back) one directory.

1.4.1. Program building blocks

1. Variables
   

   Our program may also use variables to store data during its execution. Variables are locations in memory (RAM) where we can store numbers, text, or more complex objects like an image. We give variables a name to reference it by, such as userName or cartTotal, and we can do math operations on it, as well as write it to the screen or read new values into it from the user.

2. Branching
   

   We can also change the instructions our program runs based on some condition we set. For example, if bankBalance < 0 then maybe we display an error message. Otherwise, we can withdraw some amount of money from the bankBalance.

3. Looping
   

   We may also want to take advantage of looping to do a set of instructions repeatedly, possibly with some variables changing each time through the loop. An example for this could be to loop over all of a student's assignmentGrades, adding up all the points so we can find an average.

1.5.1. ASCII

1. Storing all the languages of the world
   

   

   Figure 4: A screenshot of a Japanese computer terminal showing C:¥ instead of using a slash.

   With early computers in other countries, people distributing the computers would have to figure out which symbols to replace from the original ASCII, and what with. This is why a command prompt in Japan still uses the Yen sign for pathing, instead of slash \ ; the Yen sign was needed more than a slash was, so it was replaced.

   This swapping of codes for different symbols also made translation and internationalization of software a pain in the butt! The same codes used for different symbols, you would have to make sure your files were saving and loading with the right country-based encoding standard!

1.5.2. Unicode

1.5.3. Color and images

1.5.4. File formats

1. HTML - Basic webpage structure
   

   Now that we know how to represent text on a computer, we can create files that contain text. If we come up with rules on what different parts of the text file means, we can make a file type like HTML. An HTML file is just text, but different items mean different things:

   <h1>My Homepage</h1>
   <p>Welcome to my homepage!</p>
   <hr>
   <p><img src="web-assets/gifs/barraconstruction.gif"></p>
   

   On its own, HTML doesn't mean anything, but programmers have created a program that reads HTML text and turns it into formatted text, graphics, and colors - a web browser (like Edge, Firefox, Chrome, or Safari) turns HTML into a usable web page.

   You could make your own website building language and your own website viewing software if you wanted to, but at this point in history HTML and HTTP has pretty much won that war.

2. CSV - Comma-separated value tables
   

   Another filetype that's commonly used are CSV files (Comma separated values). The file's contents looks like this:

   GAME,GENRE,YEAR
   Super Mario Galaxy,Platformer,2007
   Metroid Prime,First person puzzle/shooter,2002
   Half-Life,First person shooter,1998
   

   But can also be read by a spreadsheet editor:

   

   Figure 7: Screenshot of a spreadsheet with column headers Game, Genre, and Year, and a set of 3 rows beneath that of some different games.

3. Source code
   

   And, most importantly for us right now, a program's code is also just a big text document. We use a special program called a compiler to convert code into binary, and then the computer knows how to run it.

   C++ source code:

   #include <iostream>
   using namespace std;
   
   int main()
   {
       cout << "Hello, world!" << endl;
       return 0;
   }
   

   Program running:

   

   Figure 8: Screenshot of a C++ program running in the terminal. It shows the message 'Hello world!' and a return code of 0 (no errors).