In this first lab exercise, the primary aim is for you to familiarize yourself with the process of creating, compiling and executing simple C programs.
The material you will need to know can be found in week 1 lecture notes.
This exercise will simply ensure you are capable of writing a small program and getting it to run.
There are no marks for this week's work, but you should practice testing and submitting your answers in preperation for future weeks.
Before the lab class finishes, you should demonstrate your work to the tutor. If the tutor says that it's OK, then you should submit it using the give command.
Once you've done this, you are free to explore some other unix commands.
One student from each pair should log in (take turns to do this).
You have been allocated a CSE account. Your CSE username will be your zID (z1234567). Login into your CSE account with your zID and zPass.
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. 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)
pp 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 27 February 12:15:20 AEDT 2017Now we're going to learn about some commands for working with directories (directories are often called folders on other operating systems).
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/DesktopThis means that I'm in the Desktop directory inside my (z7654321's) home directory and my home directory is stored on the fileserver 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.
lsThe 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/z7654321If 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 public_htmlThe 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 lab01Now the command
ls should show you the directory you just created.
ls Desktop lab01 public_htmlNow we will use
cd in a slightly different way where we tell it what directory we want to change into
cd lab01To confirm we really are in our new created lab01 directory type the
pwd command again.
pwd /import/cage/1/z7654321/lab01If all this has worked, it's time to try compiling your first program!
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 acheived by simply highlighting with the left mouse button and pasting can be acheived 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.
If it is not displaying line numbers, go to the Edit->Preferences menu item and check the 'Display Line Numbers' option.
Once you have pressed saved, click on the Terminal window again and type this command to compile your program:
dcc -o bad_pun bad_pun.cThe
-o bad_pun option tells the compiler to give
the 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
Press 'q' to exit man.
Run the program to test that it works. Type:
./bad_punThe
./ 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:
~cs1511/bin/autotest lab01 bad_pun.c Test 1 (./bad_pun) - passed 1 tests passed 0 tests failedDon't worry if you fail the check - and you can't see why.
cp to copy bad_pun.c to a
new file named bird.c, like this:
cp bad_pun.c bird.cYou 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 repeatedley 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
~cs1511/bin/autotest lab01 bird.c Test 2 (./bird) - passed 1 tests passed 0 tests failedAgain don't worry if you fail the checking - and you can't see why.
kangaroo.c from the course account to your
directory by typing (make sure you type the dot at the end):
cp ~cs1511/public_html/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.cYou 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~cs1511/bin/autotest lab01 kangaroo.c Test 3 (./kangaroo) - passed 1 tests passed 0 tests failedAgain don't worry if you fail the checking - and you can't see why.
If you don't have a computer where you live, you will need to spend time in CSE's labs outside scheduled lab classes. You can check lab availability here.
If you finish the above exercises within your lab-time and/or your partner has a laptop with you, try following the instructions on the course home page for home computing to set it up so you can work on COMP1511 on your own computer.
It's useful to try and set up your laptop (if you have one) in 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.
You submit your work with the give command like this:
give cs1511 lab01 bad_pun.c bird.c kangaroo.cor you can upload the relevant files to give if you are working from home.
In future weeks both members of each lab pair need to submit your work using give
every week and you need to show it to your tutor together for assessment.