CSCI-203 Lab 2 Fall 2002
Before getting started you should setup an edit window for constructing a lab handin.txt file. The idea is that as you go through the lab, whenever it is indicated that something must be handed in, you can just copy and paste it from your terminal window into the handin.txt edit window. At the end of the lab you save the handin.txt file, print it, and then hand it in. If you aren't quite finished at the end of lab then you can save the file anyway and then when you return to finish the lab open an editor window and load the partly finished handin.txt file.
Every handin.txt file must start with a header containing your name, lecture section, lab section, date, etc. At this point open an edit window in emacs by pulling down the Files menu and choosing Open File.... This should bring up a directory path in the minibuffer to which you can append the file name banner, the file you are going to create. Create a banner by entering the following form:
//#################################################### // Name: Happy Student // Course : CSCI 203 / Prof. LectureProf / MWF ?:00 // Lab Section: Monday 6-8AM Section Number: nn // Assignment: Lab #?, or Project #? // Date: mm/dd/yy // //####################################################Make the appropriate changes, and save this file. Having done this, you should not have to repeat the construction.
Now to begin a handin.txt file for Lab 2, open a new edit window for a file named handin.txt. Insert the banner file by invoking the Files menu and selecting Insert File.... Enter the name of the banner file, i.e., banner. You should repeat this process at the beginning of every laboratory session. Now save this file as it currently is. Retain this edit window in the corner of your workspace so that when instructed you can copy data into it, thus gradually building up the file which you print and hand in.
Do the following at the Unix prompt ``%'';
home cp ~cs203/dotfiles/.cshrc . source ~/.cshrcThis updates your .cshrc file so that you can print a file using the print command which does not print a header page. Saves toner and paper!
Now, on to the lab exercises...
As you progress through the semester you will be creating a lot of files. As a means of keeping your account organized, UNIX provides the ability to create a special file known as a ``directory'' -- on a PC or Mac you may know these as ``folders''.
In computer file systems, directories are organized in a hierarchal fashion. Your account is, itself, a directory which is most often referred to as your home directory. In the directory hierarchy of Bucknell's file system there is a directory named ``student'' which contains 26 more directories named ``a'' through ``z''. Each directory named for a letter of the alphabet contains all the home directories of students whose account names begin with the respective letter. For instance, the student John Smith might have his directory in ``s'', if his account name is ``smith''; if, on the other hand, his account name is ``jsmith'', then his home directory would be in the directory ``j''.
Each directory in the file system can contain several other directories. We refer to a directory within a directory as a ``sub-directory'' of the higher level directory and the higher level directory as the ``parent'' of the sub-directory. For example, if your home directory were named ``jsmith'' it would be a sub-directory of the directory named ``j'', and j would be the parent directory of your home directory.
Recall that a directory is just a special type of file. It should not surprise you that a directory can contain text and other types of files as well as numerous directories. In this lab, you will create and use directories and sub-directories to help you keep your account organized; while this may not seem like a major issue at the moment, by the 4th or 5th lab you will have come to appreciate this simple yet powerful concept.
Open a terminal window and at the UNIX prompt issue the ``ls'' command. You will probably only see the files you worked with last week.
Enter the following two commands at the terminal window's prompt.
mkdir cs203and then
mkdir CS203List your home directory again and you should see the following:
CS203/ cs203/These entries illustrate two points. First, the ``/'', forward slash, character at the end of a file name indicates that the file is a directory. Note: this character ``/'' is not part of the file name! It is added to emphasize that the file is actually a directory. Second, UNIX distinguishes between upper and lower case letters; which can be annoying if you think you typed something correctly, but you substituted a lower case letter for an upper case one or visa-versa. One popular convention for naming files is to capitalize the first character of directory names and use a lower case letter for the first character of all other kinds of files. This makes it easy to distinguish the directories from files of other types.
Since you only need one directory for your course work, delete one of the directories by issuing the following command.
rmdir cs203In future labs we will always refer to your CS203 directory as the place where your work for the course is kept.
Knowing how to use directories and sub-directories and being able to manipulate the files in them will prove to be useful throughout this course. In this section of the lab you get a lot of practice with UNIX and hopefully a clear understanding of the file system. Now, read through all of sections 4.3 and 4.4 of The Guide and do the examples as indicated. Be very careful to watch for error messages which may occur -- these are an indication that things didn't go as intended. Also, make frequent use of the commands ls, to determine directory content, and pwd, to determine your current working directory. In fact, do these two instructions now to see what they tell you.
Do sections 4.3 and 4.4 in The Guide.
When you have completed all the examples be sure you are in your home directory (use pwd command). If you aren't there issue the cd command with no directory argument. Now that you are in your home directory issue the following command:
ls -RCool, huh? The -R option instructs UNIX to recursively descend through the directories and perform the specified action, ls in this case, in each subdirectory.
Open your handin.txt file and, using the Copy and Paste keys you learned about last week, (these keys are on the left side of the keyboard), copy the data generated by the above command ``ls -R'', into your emacs window. What you need to copy begins with:
host-name#% ls -RAnd ends with:
host-name#%
Having copied the data to the handin.txt window you should put a header on the copied data. Skip a couple of blank lines after the banner and then add 5 lines as follows (before your data)
//####################################################### // // Exercise 1 // //#######################################################If you are unsure that things have gone as they should, have your professor or TA verify that you have done this correctly.
The time will come when you want to delete a directory for one reason or another. In section 4.3 of The Guide, you learned how to remove, delete, files with rm. Using this same command you can also remove directories, including all the sub-directories and files they may contain; can you guess why rm should be used with caution? Try the following:
rm progsThe message you see informs you that progs is a directory and just using rm will not delete a directory. The rm command used in conjunction with the option `-r' instructs the system to delete all the files in a directory (including any subdirectories) and the directory itself. Issue the following command:
rm -r progsThe system asks you if you want to look into the directory progs, respond with ``y''. Next the system asks you if you want to delete the file named
jack_theory, reply with
``n'', then respond with ``y'' when asked if you
want to remove progs. Because you instructed the system not
to remove the file jack_theory, the directory is not empty and
the system will not delete it even though you instructed it to. This
helps to guard against deleting files and directories accidentally.
Go ahead and issue the
rm -r progscommand again only this time answer with a ``y'' to all prompts. Now remove the labs directory and all its contents (this only requires one command). Next remove the file ``myhumpty'' from your home directory.
Using your newly gained knowledge:
CS203/Labs/Lab1 directory.
Today you get your first ``real'' experience with a program. Turn to page 60 in Mercer (your textbook), and read and do Programming Project 2A. To create a new file, open emacs and in the Files menu, select Open File.... Correct the directory path given in the minibuffer if necessary to indicate to your Lab2 directory. Append hello.cc to the directory path in the minibuffer, making sure that a slash (/) separates the file name from the preceding directory names. Enter the program as it appears in the textbook and save it. Make sure, your terminal window is in the correct directory. Now compile this file by typing at the Unix prompt:
g++ hello.cc -o hello.exeand press return. This instructs the system to compile the program in the file hello.cc and create an executable named hello.exe -- in other words, the compiler translates the program description in hello.cc into a machine language program which it puts in the file hello.exe. It is not important that you understand this g++ command completely just yet -- you will get a lot of experience with it this semester. If you have entered everything correctly, there will be no error messages printed from the compiler. If you have error messages, compare what you typed to what is in the text, make any corrections, save the file, and recompile it. Once the program compiles without errors, continue.
Type the following at the system prompt:
hello.exeIf all has been entered correctly, you should see the words
Hello world!appear on the screen. If not, raise your hand and have your professor or TA assist you.
Now complete the following activities using hello.cc as a base. (Recall that we used endl in the output statement (cout) to cause the screen output to go to a new line. You will need to use this to cause the output to have the appropriate blank lines.)
Open the handin.txt edit window and create a new header (actually, just copy and paste the ``exercise 1'' header and change the name). Label this new header ``hello.cc''. Copy this enhanced ``Hello World'' program code to your handin.txt file along with the output from a test run of the program. (Use the insert file option from the Files menu to put the program code in and then do copy and paste to transfer the result of the execution.
To give you more practice with the error messages that a compiler might give you, we have modified Lab Project 1C from the Mercer text. Before you begin, issue the command
pwdto see what your current directory is. The response to the command should be something like the following.
.../loginname/CS203/Labs/Lab2If you don't see this then get your instructor's or TA's attention and ask for help.
Now to begin: you will need another file, errors.cc. Copy
this file from ~cs203/Labs/Lab2 into your own
Lab2 directory.
Below is a series of steps to be performed along with some questions that you will need to answer. To answer the questions, create a file named exercise-2, using emacs. Type the answers as you go into the handin.txt edit window -- you should make a new header and label it ``errors.cc''.
errors.cc. Give a brief explanation of
what the program does. In particular, what does the third line in
the output indicate?
Note: Since this file is short, it will be easy to make changes based on line number by just counting the lines. With larger files, this is more difficult. To move to a specific line in a file, type C-c g. After entering that command, type in the line number in the minibuffer. The cursor will then jump to that line.
Note: you should undo each change before moving on to the next part.
// in front of {.
<'' from the line#include <iostream>
<< with >> in line 9.
() after the word main with a
; in line 3.
As a precaution you should save your handin.txt file at this time. Don't close the window because there is more to come, but it is a good habit to save your edit sessions frequently.
// A happy face drawing program
#include "/home/hydra/COURSES/cs203/include/Face.h"
int main ()
{
// create a Face object called
// myFace
Face myFace;
myFace.Display(); // a call to a member function
pause();
return 0;
}
Save the program as face.cc. The #include allows you
to use some code that we wrote. The include file defines the
class Face.
Compiling the program actually involves two activities. First, the program in face.cc is translated into machine code. But before it will work, the translated version must be linked together with other translated code for the Face class. Both activities are specified in the same command. To compile, enter the following command line.
g++ face.cc -L/home/hydra/COURSES/cs203/lib -lSamba -o face.exeThe -L phrase specifies where the compiler should look for the other translated code, and the -l specifies the name of the file (called a library) which contains the code.
To save retyping that long line, you can retrieve the line at a Unix prompt by pressing the up-arrow key. Now you can edit the line using the left and right-arrow keys. If this does NOT work, ask your TA or instructor for help.
To run this program you must type the following at a UNIX prompt.
face.exe | sambaThe vertical bar is called a pipe. What this pipe does is to direct the output of your face.exe program to the input stream of the samba program. The samba program will produce the nice graphical output. You should see a new window with Samba at the top. Move this window down and you should see a little window that says Polka Control Panel. Press Start on the Polka Control Panel. You should see a pretty face.
Before leaving this program try the following. Execute the face.exe program on its own, without piping the output to samba. In other words, just enter the following command at the UNIX prompt and see what is displayed.
face.exeWhat you will see is several lines of strange looking output which is exactly what was piped into samba. The lines you see are actually instructions which the samba program inputs and carries out.
Save your handin.txt file at this point. You might want to look it over to make sure that what is there is in a nice format and that nothing is missing.
Print this file using the new a2ps command you learned last week.
a2ps handin.txt