Due 11:59 PM, Monday, January 22, 2018
To log in: % ssh yourlogin@classroom.cs.unc.edu
Note that when logging in to the classroom.cs server, your password is not echoed onto the screen (not even *s are shown). Simply press [Return] after your password.
To copy file from laptop to server: % scp file_on_laptop yourlogin@classroom.cs.unc.edu:comp411lab/ To copy file from server to laptop: % scp yourlogin@classroom.cs.unc.edu:comp411lab/file_on_server ./
Prior to beginning this tutorial, complete the following readings:
Log in to classroom.cs.unc.edu. Before starting work, execute the following command to start a command interpreter ("shell") called bash, and initialize some settings to values that are convenient for our class. (You should type the following command each time you log in, for all the labs in this semester, just to ensure a predictable environment for you to work in. Moreover, for subsequent labs, the environment settings may be updated, so it is best to run this command each time you log in.)
/home/porter/comp411/bin/comp411start
Next, create a subdirectory (i.e., folder) comp411lab in your home directory by typing the following commands. Note: In these instructions, the % at the beginning of every line is simply the prompt that the command interpreter prints for you. Your prompt may look different, e.g., classroom(nn)%, where nn is the sequence number of the command you are typing. So, in the following, you are only to type whatever is shown after the % prompt.
% cd ~ % mkdir comp411lab
You must protect this folder so others cannot see inside it. You use the filesystem command (fs) to set up an access control list (ACL) that allows nobody any access (-clear) except you (all access). Be sure to replace yourloginname with your actual login id.
% fs setacl -clear -dir comp411lab -acl yourloginname all
Inside it, create a subfolder lab1 and make it your current working directory:
% cd ~/comp411lab % mkdir lab1 % cd lab1
Download/copy the sample program intro.c into the lab1 subfolder. You can do this in either of two ways. One option is to download the file on your laptop using your browser, and then use a secure copy tool. Here's how you do it, depending on your operating system:
% scp path-to-download-folder/intro.c yourlogin@classroom.cs.unc.edu:comp411lab/lab1
The second method is to simply login onto classroom, and then copy the file from a location on that server itself, using the copy (cp) command, as follows:
% cp /home/porter/public_html/courses/comp411/s18/lab1/intro.c .
For this tutorial, you will edit files using the editor pico (actually, it is mapped to a clone by GNU called nano, but you can use either name to launch it). View the C file using using pico as follows:
% pico intro.c
This editor is text-based, and you will need to use Control-key combinations to navigate the menu. Here are a couple of useful pico references:
Quit the editor, and enter the following Unix command to compile the program:% gcc intro.c
Or,
% cc intro.c
Note: cc stands for "C Compiler", which on our department's systems is linked (i.e., aliased) to gcc, which is the GNU C Compiler, an open-source implementation.
What do you think has happened? Have a look at the contents of your current working directory. Find out what type of data is contained in the file a.out (Hint: use the file command you learned in the Unix Tutorial Lab 1).
Execute the program by typing
% ./a.out
and see what happens. Do you understand the C text of the program?
NOTE: always put a "./" before the program name when executing a program in your working directory.
Remove the file a.out and try compiling the program in a slightly different way:
% gcc intro.c -o intro
What is the difference? Can you run the program now? Run the program again, but this time redirect its output into the file intro.out (using ">" to redirect its output, as described in the Unix Tutorial). What has happened to the prompting message? Have a look into the file intro.out and make sure that you understand what is there and why. Create file intro.in with a value of the radius and run the program so that it takes its input from intro.in and writes the output into intro.out:
% ./intro < intro.in > intro.out
Carefully note the syntax of the above command to run the program with its standard input redirected from a file, and its standard output redirected to a file. The order of the two files does not matter, so ./intro > intro.out < intro.in would also be okay, but listing the input file first makes the command easier to read. Note however that intro.in > ./intro > intro.out is not a correct way to accomplish the same.
Modify the program so that it prompts you to enter the radius value as input in centimeters using the prompt "Enter radius (in cm):\n", but displays the result in square inches. (One inch is 2.54 cm exactly.) Use pico to edit the file to make this modification, and save the file as ex1.c inside your lab1 subfolder under the comp411lab folder in your home directory.
Compile this program and run it on a couple of different inputs to verify that it is working correctly. The inputs and outputs can be from the keyboard/terminal; you do not need to use redirection of input/output from/to files for this exercise. Here is an example execution scenario (user input is shown in red, and program output in blue):
% ./ex1 Enter radius (in cm): 2.54 Circle's area is 3.14 (sq in).
Copy the file ex1.c to ex2.c (so you do not accidentally edit ex1.c any further). Modify the program in ex2.c to also compute and display the circumference. Here is an example execution scenario:
% ./ex2 Enter radius (in cm): 2.54 Circle's area is 3.14 (sq in). Its circumference is 6.28 (in).
Copy the file ex2.c to ex3.c. Modify the program in ex3.c to make it work on multiple inputs. In particular, it should repeatedly ask for a radius value (in centimeters), and print the corresponding area (in square inches) and circumference (in inches), until the user enters the value 0 as radius. At that point, the program should print the area and circumference (both 0), and then terminate.
Compile this program and run it, feeding it several radius values from the keyboard, and verifying that the values it displays are correct. A single run of the program should be able to compute as many of these calculations as you want, until you enter 0.
% ./ex3 Enter radius (in cm): 2.54 Circle's area is 3.14 (sq in). Its circumference is 6.28 (in). Enter radius (in cm): 5.08 Circle's area is 12.57 (sq in). Its circumference is 12.57 (in). Enter radius (in cm): 0 Circle's area is 0.00 (sq in). Its circumference is 0.00 (in).
Sample inputs and corresponding outputs are provided under /home/porter/comp411/samples/lab1. You should try running your program on the sample input files provided, and make sure the program's output is identical to that in the sample output files. For example, the sample input files for Exercise 1 are called ex1in1 and ex1in2. Their corresponding outputs are in the files ex1out1 and ex1out2. You can, of course, manually type or cut-and-paste the contents of the input files onto your terminal when running the program. Or, you could feed that sample input to your program using input redirection (./ex1 < ex1in1). To verify that your program is working correctly, compare its output to the test output provided. Again, you could do this comparison manually, or you could use a very useful UNIX command called diff.
The full sequence of steps to run your program and verify its output is as follows. First, copy the sample input and output files to your lab1 folder:
% cd ~/comp411lab/lab1 % cp /home/montek/comp411/samples/lab1/* .
Then do the following:
% ./ex1 < ex1in1 > ex1result1 % diff ex1result1 ex1out1
The diff command prints any differences it finds between your program's output (which you redirected into the file ex1result1) and the correct output provided to you (in the file ex1out1). Only those lines that do not match are shown. Each line in the output is prepended with "<" if it belongs to the first file, and with ">" if it belongs to the second file. See Wikipedia page on diff for more information.
The variation diff -y prints the two files side-by-side (the first one on the left, the second on the right), and highlights lines where they differ. Watch out for extra spaces at end of lines, etc.!% diff -y ex1result1 ex1out1
If you only want to see the lines that differ, you can use the following command:
% diff --suppress-common-lines -y ex1result1 ex1out1
If there are no differences, it prints nothing.
Before submitting your work, be sure that your compiled program runs correctly on all of the sample inputs provided exactly, i.e., diff produces no output at all. You may receive zero credit if your program's output does not exactly match the sample outputs provided. For example, for Exercise 1, two input files are provided: ex1in1 and ex1in2. Their corresponding outputs are also provided: ex1out1 and ex1out2. To check that your program works correctly on both, you may do the following:
% ./ex1 < ex1in1 > ex1result1 % diff --suppress-common-lines -y ex1result1 ex1out1 % ./ex1 < ex1in2 > ex1result2 % diff --suppress-common-lines -y ex1result2 ex1out2
Once you become familiar with diff, you may prefer to invoke it simply without any of the modifiers:
% ./ex1 < ex1in1 > ex1result1 % diff ex1result1 ex1out1 % ./ex1 < ex1in2 > ex1result2 % diff ex1result2 ex1out2
If neither of the diff commands showed mismatches between your program's output and the desired output, then your program is assumed to work fine. If your output happens to have one or more extra space characters at the end of a line, they can be hard to tell. In that case, use the hexdump -c command to display all the characters in your file:
% hexdump -c ex1result1
The hexdump -c command will show all spaces (as spaces), tabs (as \t), newlines (as \n), returns (as \r), etc., thereby making it easier to see whitespace characters.
Repeat such tests for Exercises 2 and 3 using all the input and output sample files provided for each.
Your assignment must be submitted electronically by 11:59pm on Friday, January 19.
You will submit your work on Exercises 1, 2 and 3 (not Exercise 0). Specifically, only the files ex1.c, ex2.c and ex3.c will be collected.
How to submit: Navigate to the folder where these files are stored (~/comp411lab/lab1), and run the following command for electronically submitting them:
% cd ~/comp411lab/lab1 % /home/porter/comp411/bin/submitlab1
When you invoke the submit script, it performs a quick check of your work (including compiling, running and comparing the output of your program with the expected output, for all sample input/output files), and provides a quick summary of any errors. Your work is submitted regardless of whether errors were found or not, but you are free to fix any errors and submit again.
If you would like to run a quick check script without submitting your work, you may run it as follows:
% cd ~/comp411lab/lab1 % /home/porter/comp411/bin/selfchecklab1
In case of any problems, please contact the instructor or the TAs on Piazza.
Last updated: 2018-02-17 11:48:55 -0500 [validate xhtml]