Week 01 Laboratory Exercises

In this Lab, you will:

• Learn how to access your CSE account
• Become familiar with the Linux environment
• Use a text editor to create small C programs
• Use dcc to compile a C program
• Run a C program in a Linux terminal

Since the course this term is partly online, you may need to work on your own computer.

Don't worry about the age or specifications of the computer itself, even reasonably old computers will be able to handle the work we're doing in COMP1511.

If you don't have a computer where you live, please contact cs1511@cse.unsw.edu.au and we'll see what we can do to help.

It's useful to try and set up your laptop (if you have one) during a lab class because your tutor or other students may be able to help you with any problems.

Otherwise, try to set up your laptop and/or desktop this week so you can work on COMP1511 at home.

This term, you will need to use VLab to connect to CSE. There's more information about how to do that at the Home Computing link.

To log in, you use your zID (which looks something like z1234567) and your zPass (which is used to log into all other university online services).

The CSE labs use the Linux operating system (not Windows or OSX or ...).

When you log in, by default, you'll be using the xfce4 window manager, and you'll see a linux desktop.

If you are asked to select a panel click on Use default config, as in the image below.

Along with menus that you can see, such as the Applications Menu in the top left corner, it also has a simple menu you can access by right-clicking anywhere on the desktop.

Have a look around and see if you can work out how to open a web browser.

Although there are lots of things you can do by using the graphical user interface (GUI) - clicking on menu items and icons, we really want you understand how to use the Linux command-line.

If you get stuck with any of this, don't hesitate to ask one of your tutors for help, that's why they're here!

If there isn't a terminal open, right click on the desktop and select 'Open Terminal Here'

This will bring up a window where you can type in Linux commands.

There are a few commands that you can use to check your account details:

• rquota tells you how much of your disk quota you've used up (from creating files)
• acc tells you your name, what classes you're in, where your home directory is and other details that may or may not be useful

Each of these is a command, and when entering into your terminal, you need to press enter (or return) after each command. Try the two we just mentioned above.

Now try running the command date - which prints the current time and date.

You should see something like this:

date
Monday 26 February  12:15:20 AEDT 2018

Now we're going to learn about some commands for working with directories (directories are often called folders on other operating systems).

• pwd
• ls
• cd
• mkdir

The Linux command pwd tells you what directory you are in, often called your current working directory.

pwd stands for 'print working directory'.

If your username is 'z7654321', and you enter the 'pwd' command into the terminal, it might tell you:

pwd
/import/cage/1/z7654321/Desktop

This means that I'm in the Desktop directory inside my (z7654321's) home directoryand my home directory is stored on the file server called cage.

What does pwd print for you?

The Linux command ls prints a list of the files in the present directory. Since you have a new account there will probably be nothing in your Desktop directory.

ls

The Linux command cd is a command that you can use to change your directory.

If you type in cd on its own as follows, you will move into your home directory.

Try this out and confirm your directory has changed by running pwd again.

pwd
/import/cage/1/z7654321/Desktop
cd
pwd
/import/cage/1/z7654321

If you run ls you'll see what is in your home directory. Since you have a new account, your home directory will most likely only contain your Desktop and a directory called public_html (which is where you can create files to create websites).

ls
Desktop Documents Downloads Music Pictures public_html Videos

The Linux command mkdir makes a new directory. To use it you must supply the name of the directory you wish to create. Lets use it to create a directory for this week's lab exercises.

mkdir lab01

Now the command ls should show you the directory you just created.

ls
Desktop lab01 public_html

Now we will use cd in a slightly different way where we tell it what directory we want to change into.

cd lab01

To confirm we really are in our new created lab01 directory type the pwd command again.

pwd
/import/cage/1/z7654321/lab01

If all this has worked, it's time to try compiling your first program!

Now it's time to create a file. We are going to use the text editor gedit.

1511 setup

To create a file using gedit, type:

gedit bad_pun.c &

This will open up a graphical editor where you can manipulate text.

Adding the & to the end of a command allows the GUI to return control to the terminal as soon as it starts (i.e. run in the background) rather than after it is closed. If you forget the &, you will not be able to type commands into the terminal until the GUI application is finished. This is always a good idea when running a command which invokes a graphical user interface (GUI).

Here's an example of a simple C program. Copy it into the gedit window, and save it.

// A simple C program that attempts to be punny
// Written 23/2/2017
// by Angela Finlayson (angf@cse.unsw.edu.au)
// for COMP1511 Lab 01 Exercise 1

#include <stdio.h>

int main(void) {

    printf("Hello, it is good to C you!\n");

    return 0;
}

When you save, it will place the contents of the editor into the file bad_pun.c.

Handy Tip 1: On many linux systems copying can be achieved by simply highlighting with the left mouse button and pasting can be achieved by simply clicking with the middle button.

Handy Tip 2: Make sure gedit is displaying line numbers down the left hand side. This is important for when we need to fix compile time errors.

The easiest way to set this up is by running 1511 setup in your terminal.

You can also change whether line numbers are displayed by going to the Edit->Preferences menu item and selecting the 'Display Line Numbers' option.

Once you have pressed save, click on the Terminal window again and type this command to compile your program:

dcc -o bad_pun bad_pun.c

The -o bad_pun option tells the compiler to givethe newly compiled program the name bad_pun.

Test what happens if you leave the -o bad_pun option out. What is the default name dcc uses?

You may wish to use the rm command to delete (remove) the file created.

(You can Google rm or rm linux if you are not sure how it works).

If dcc does not print out any error messages, then your program has been successfully compiled. Otherwise you will need to find the errors in your code, fix them, save the file and compile again.

Handy Tip 3: Look for the line numbers that are displayed in the error messages as they are major clues to where the problem is in your code.

Handy Tip 4: Always start with fixing the first error first. Sometimes fixing one compile error, saving and recompiling can make all or some of the other errors go away!

After successfully compiling you can check that dcc has produced an executable by typing ls -l and looking for a newly-created bad_pun file (check the file creation time to see if it really is new).

A useful Unix command is man short for manual. Find out what the -l option for the ls command you used before does. Type:

man ls

In the manual page you can scroll using your arrow keys on your keyboard. Press 'q' to exit man.

Run the program to test that it works. Type:

Press 'q' to exit man.

Run the program to test that it works. Type:

./bad_pun

The ./ before the program name specifies that the program is found in the current directory. Note that Unix executable (program) names do not require the .exe extension that you might have have seen under Windows.

The COMP1511 class account contains a script that automatically checks your solution to lab exercises.

While it is not important this week, lets run the autotest script so you can see what it does.

You can check bad_pun.c like this:

1511 autotest bad_pun bad_pun.c
Test 0 (./bad_pun) - passed
1 tests passed  0 tests failed

Don't worry if you fail the check - and you can't see why.

There are no marks for this week's lab but practice submitting your work electronically.

You submit your work with the give command like this:

give cs1511 lab01_bad_pun bad_pun.c

In future weeks both members of each lab pair need to submit your work using give.

1511 setup

Now use the Linux command cp to copy bad_pun.c to a new file named bird.c, like this:

cp bad_pun.c bird.c

You are now ready to start editing the file bird.c using your favourite editor.

gedit bird.c &

Note that the basic structure of the program can be retained; you just need to change the comments, and modify and/or add printf statements to the program. Edit the file bird.c to produce a new program that behaves as follows:

dcc -o bird bird.c
./bird
  ___
 ('v')
((___))
 ^   ^

Make sure you save your modified program before you compile it.

Make sure you re-compile your program every time you modify the code.

Handy Tip 5 : Linux remembers the commands we have recently typed in. By pressing the UPARROW key, it will bring up your previous command and save you retyping it in! Try it. You can press the UPARROW key repeatedly to go back to the second last command, third last command and so on.

Handy Tip 6 : At your Linux command prompt, type in ./b and then press the tab key. Linux will automatically try to fill in your partially typed command for you!

Again try the automatic checking script in the class account.

1511 autotest bird bird.c
Test 0 (./bird) - passed
1 tests passed  0 tests failed

Again don't worry if you fail the checking - and you can't see why.

There are no marks for this week's lab but practice submitting your work electronically.

You submit your work with the give command like this:

give cs1511 lab01_bird bird.c

In future weeks both members of each lab pair need to submit your work using give.

1511 setup

Copy the program kangaroo.c from the course account to your directory by typing (make sure you type the dot at the end):

cp ~cs1511/public_html/21T1/tlb/01/kangaroo.c .

The dot '.' is a shorthand for the current directory and there is a space between kangaroo.c and the next dot. You can check that the file has been copied by typing:

ls
bad_pun bad_pun.c bird bird.c kangaroo.c

You can examine the contents of the file by typing:

less kangaroo.c
// A simple C program that prints an ASCII kangaroo
// Written 7/3/2017
/  by Andrew Taylor (andrewt@unsw.edu.au)
// as a lab example for COMP1511
...

(less is an improved version of an earlier utility called more, which shows you long text files one page at a time and allows you to go forward and back using the space bar and the 'B' key. Less is more! Press 'q' to exit less.)

Now try to compile kangaroo.c. You should see a list of confusing error messages.

dcc -o kangaroo kangaroo.c
kangaroo.c:4:1: error: expected identifier or ‘(’ before ‘/’ token
 /  by Andrew Taylor (andrewt@cse.unsw.edu.au)
...

Your job is to fix the errors.

You'll need to use an editor to change the file kangaroo.c

Run gedit like this:

gedit kangaroo.c &

When you have fixed all the errors you should be able to do this.

dcc -o kangaroo kangaroo.c
./kangaroo

  /\   ___
 <__\_/    \
    \_  /  _\
      \_\ / \\
        //   \\
      =//     \==

Hint: the error messages are confusing but they usually indicate where the problem is.

Hint: treat it as a puzzle. Look for differences between your program and the working programs you have been shown.

Hint: all the errors but one involve a single missing character.

Hint: if it looks like there are too many backslashes in the program, it is correct. Don't delete any backslashes (you do need to add one backslash). It was mentioned in lectures that the backslash has a special interpretation in C.

Again try the automatic checking script in the class account.

1511 autotest kangaroo kangaroo.c
Test 0 (./kangaroo) - passed
1 tests passed  0 tests failed

Again don't worry if you fail the checking - and you can't see why.

Submit your work with the give command like this:

give cs1511 lab01_kangaroo kangaroo.c

In future weeks both members of each lab pair need to submit their work using give.

Your tutor has sent an email to your official UNSW email account. You need to reply to it. We want to make sure you can receive official emails!

You can ask any questions you have related to COMP1511 on the course forum.

Remember never to post assessment code on the course forum. Course staff can view your recently autotested/submitted code. You can also post anonymously, by clicking on your profile icon in the top right, then click on your zID, then click on "Enter Anonymous Mode".

To make sure that you can access the course forum, please post a reply to the "Welcome to COMP1511! :D Introduce yourself!" topic introducing yourself (and optionally a pet/food picture or a picture that tells us something about you!).

Take a look around the forum! Student Page.

CSESoc is the School's Constituent Society. This means that by doing COMP1511, you're automatically a member!

CSESoc runs a an event most terms to introduce COMP1511 students to the computing infrastructure of the school. It's also an opportunity to meet new people. The event is running Tuesday the 1st of June from 3pm - 5pm.

Where/When: Tuesday the 1st of June from 3-5pm in Tyree G16 Link to register: here Link to Facebook event: here

A Message of the Day (often called an "MotD") is a message traditionally shown when you log into a unix system. It usually gives you a warm greeting and tells you some information.

In this exercise, you will make your own MotD. You do not need to submit it, nor is it directly assessed in any way. It is, however, an opportunity for you to demonstrate your creative skills to your new friends and tutors. You can even keep adding to it throughout the term.

To get started, run the following command. It will show the following output.

1511 motd
Did not find a MotD! You should make a file called motd.c and compile it.

This program has just enabled an MotD on your shell, but now you need to specify what it will say.

Make a new file called motd.c in your home directory. If you're not in your home directory, type the command cd to go there.

You should make this program print out a message of the day, like "Hi Tom, I'm looking forward to COMP1511".

When you're done, you can run:

dcc -o motd motd.c
./motd
Hi Tom, I'm looking forward to COMP1511.

To get rid of the message, remove the motd file:

rm motd

Now that you've got it working, here are some ways to make your motd stand out:

• Make some ASCII text: Here's an ASCII text generator!
• Add some color to your message!
• Add some ASCII art (a time honored tradition in computing): Here's one collection - google for more!

You can run give multiple times. Only your last submission will be marked.

Don't submit any exercises you haven't attempted.

If you are working at home, you may find it more convenient to upload your work via give's web interface.

Remember you have until Week 2 Monday 20:00 to submit your work.

You cannot obtain marks by e-mailing your code to tutors or lecturers.

You check the files you have submitted here.

Automarking will be run by the lecturer several days after the submission deadline, using test cases different to those autotest runs for you. (Hint: do your own testing as well as running autotest.)

After automarking is run by the lecturer you can view your results here. The resulting mark will also be available via give's web interface.

Lab Marks

When all components of a lab are automarked you should be able to view the the marks via give's web interface or by running this command on a CSE machine:

1511 classrun -sturec