CSE 303 Homework 3

Due: Wednesday 1/23/08 11:59PM
Turnin: online - turnin instruction

FAQ

HW3 Q&A Wiki Page

Updated skeleton code for hw3D.c and hw3Dfsa.h. (1/19/2008, 12:47AM)
If you hadn't yet fetched the code as of the post time of this update, the instructions on this page have been changed so that you will be an updated set of files by following them - no need to apply the patch. If you had already fetched them, follow the link for instructions.

Added a page describing finite state machines and linked it from various places in this document. (1/19/2007 2:44AM)

Added a page explaining what 'character,' 'word,' and 'line' mean, in this assignment. (1/19/2007 3:00AM)

Overview

This assignment is an introduction to programming and "building" (compiling and linking) C programs. There are rougly a million things that can go wrong, even if all you're trying to do is build a program you know works already. It is designed to be a sequence of small steps. It is also designed so that you can read, build, and run some working code before you have to try to write, build, and run similar code yourself. The purpose of that is to let you run into whichever problems you're going to run into (and there are a billion, so it's hard to guess which ones you'll see) in small steps, and to give you an example of how to do things rather than requiring that you read rely solely on the sometimes difficult to understand man pages and other documentation.

There are eight parts to the assignment. The first is an exercise that tries to make clear what the C preprocessor does. To really understand what it does, it's useful to keep in mind that it is NOT (very) aware of what the C language is. The exercise is intended to make that totally clear.

Name	Description	Status
hw3-cPreprocessor	Explanation of the C preprocessor's function by example (plus a tiny introduction to "thinking like a Unix programmer").	Deployed.

The remaining seven parts involve implementing a sequence of programs that are very similar to the standard Unix word count (wc - man wc) program. (Note: hw3G takes a tiny step towards an implementation of sed, an editor.)

Name	Description	Status
hw3A	Straightforward implementation of word count that reads stdin only.	Skeletal - counts characters only.
hw3B	hw3A, but the user names an input file on the command line. Character, word, and line counts for the contents of that file are printed.	Skeletal - like hw3A but with some C code hinting at how to implement the "reads from a file" modification. Contains debugging output code that should eventually be removed.
hw3C	Implements a modified definition of word count - characters and words in C '//' style comments are ignored.	Unimplemented. Start from your working solution to hw3B.
hw3D	A solution to basic word count structured as a finite state machine.	Fully implemented and working. Fully implemented and working in updated hw3D files.
hw3E	hw3D modified to not count characters or words inside C '//' style comments.	Not implemented - just a copy of hw3D.

Another intention of this assignment is to show you the finite state machine approach to implementation, which can be very effective for some kinds of problems (including this one). The two colors in the table above group programs by solution style: yellow for "no particular style" and green for "finite state machine".

There are two more parts.

Name	Description	Status
hw3F	hw3E with the code broken into multiple source files.	Nothing - not even skeletal. Start with your solution to hw3E.
hw3G	Performs the word count function, ignoring characters and words in '//' style comments, PLUS outputs the input text with those comments removed.	Nothing - not even skeletal. Start with anything you want.

Not Exactly Word Count

We ususally think of word count as counting the number of characters, words, and lines in its input. If you read the documentation closely, what it counts is the number of characters, words, and newlines in its input.

We want to count the number of lines (e.g., that would appear if the input file (assuming its a file) were displayed in emacs in an infinitely wide window).

Getting Started

Get a "tar" of The Assignment Files

Copy the file /cse/courses/cse303/08wi/hw3DistV1.1.tar.gz to the directory in which you want to create a directory that will hold all the assignment files.

• If you're working in a shell running on attu, just say
  cp /cse/courses/cse303/08wi/hw3DistV1.1.tar.gz .
• If your shell is runing on a lab Linux workstation, that command may work as well. (I'm not sure whether or not that part of the file system is "mounted" on lab Linux boxes.)
• From any shell, anywhere, you can do this:
  scp yourattulogin@attu:/cse/courses/cse303/08wi/hw3DistV1.1.tar.gz .

Note the period at the ends of both of those commands.

(Note for cygwin users: scp (and ssh) aren't installed by default with cygwin. If your install doesn't have them, rerun setup.exe. Hit OK until you get to the dialog box that is offering things to install. Hit the View button in the upper right until you see an alphabetized list of all available packages. Look for openssh (I think it is...). Click on the "Not Installed" (I think it is -- all the way on the left) and it should change to a version number. Now hit OK and openssh should be installed, providing you with scp and ssh commands.)

Check What untar'ing Will Do

Run the command:

tar tzf hw3DistV1.1.tar.gz

That will print the names of the files contained inside the tar file. Those files, including directories, will be created when you untar in the next step. Note that this tar file creates a directory in which all of its files go. Not all tar files do that, so it's handy to check before untar'ing so you don't end up with 1500 files in the current directory when that's not what you wanted.

untar

Run the command:

tar xzf hw3DistV1.1.tar.gz

That will create a directory hw3Dist containing some other directories containing some files.

Guide to Starter Files

Directories

• hw3-cPreprocessor: has the preprocessor exercise. Go there and rummage around.
• hw3AtoE: has source files hw3A.c, hw3B.c, etc. Their status is described in the table above. It also has a shell script, run, described below, and a text file, problemFile.
• hw3F and hw3G: put all files for your solutions to those problems in this directories (in the obvious way).

The run Script

I wrote a shell script that compiles and runs all of hw3A through hw3E. You invoke it as in this example:

./run testInputFile1 testInputFile2 ...

(Of course, you have to supply the names of files that actually exist.)

For each file named in the command line, the script first runs the Unix wc program, then each of hw3A through hw3E. This is intended to help with debugging - you can conveniently compare the output of each of your programs against what wc says (remembering that our definition of the problem differs slightly from what wc actually computes). There are otherwise useless implementation files (e.g., hw3E.c) in the distribution to help simplify this script -- it doesn't check whether or not the file exists and can be compiled, it just goes ahead and tries to compile it.

You do not have to use this script. I can't imagine why you wouldn't, but if it's causing you problems you can just compile manually. To do that, issue a command like this:

gcc hw3B.c -o hw3B

If the compile succeeds, it will leave the executable in a file whose name depends on what kind of system you're running on: hw3B (Unix), or hw3B.exe (cygwin).