CSE 413 Autumn 2006

Assignment 4 -- C Warmup

The purpose of this assignment is to gain experience with basic C programming. The algorithms involved are fairly simple; the point is to become familiar with the langauge, some basic library functions, and the Unix programming environment.

1. Word Find

Write a program named wordfind that reads a file from standard input and prints on standard output each of the lines from the standard input that contains a string given on the wordfind command. For example, suppose we have the following a file named silly.txt containing the following:

   How now
   brown cow?
   
   The quick sly fox jumped over
   the lazy brown cow.

If we compile the program and call it wordfind, then enter the command wordfind cow <silly.txt, the following should be written to standard out:

   brown cow?
   the lazy brown cow.

This is the same output that the Unix program grep would produce searching for a word in a file; the difference between wordfind and grep is that wordfind searches only for exact matches of the given string, while grep can search for arbitrary regular expressions.

Your program should complain if no argument is given on the command line and return with a non-zero exit status in that case. (i.e., return a non-zero value from main if no string is supplied).

2. Word Count

Write a program named wordcount that reads from standard input and writes to standard output the number of lines, words, and characters that appear in the input. For example, command wordcount <silly.txt (using the silly.txt example file above), should print something like

  5 14 70

More specifically, the output from wordcount should match the output from the standard unix command wc on the same file.

Details

• Your programs should be able to deal with input lines of up to 1200 characters (including the trailing '\0' at the end of each input line). However, it should be easy to change this limit by changing a single number in a #define directive and recompiling the program.
• You should read the files a line at a time using gets or something similar to read each line into a string in a single operation. Don't read the input one character at a time.
• You should use standard C library functions when these are suitable; don't reinvent or reimplement them.
• For the wordcount program, "words" are defined as sequences of characters separated by whitespace (blanks, tabs, newlines, etc.). Specifically, a character is defined as whitespace if the C standard library function isspace returns true for that character.
• Your programs should deal correctly with files containing blank lines and/or extra whitespace before, between, or after words.
• Your programs should each be contained in a single source file; you don't need to deal with separate source files or header files at this point. However, you must break your programs up into functions where that makes sense, such as a function to count the number of "words" in a string. Programs that consist of a single main function are not good style.

Hints

• Develop your programs in small steps. For for example, verify that you can read files one line at a time before you try to process the lines. Verify that you can successfully search for one string in another before you try to combine the search with the rest of the wordfind program. Incremental development and testing will definitely save you time in the long run, even if it involves writing some extra code to test things.
• A debugger like gdb can be very useful for isolating problems, but never underestimate the usefulness of strategically placed printf statements for debugging.
• Command-line arguments to Unix programs, like the word on the wordfind command line, are supplied to the main program in a pair or parameters. The full specification of main is int main(int argc, char *argv[]). Parameter argc is the number parameters on the command line. The first array element argv[0] is, by convention, the program name (wordfind), so the number of arguments will always be at least 1.
• There are some good examples of character processing in Kernighan and Ritchie's The C Programming Language. Feel free to adapt anything you find there (or find elsewhere), but you are ultimately responsible for every line of code in your program. You should be able to explain all of the code, and you should be able to solve similar problems in the future on your own. Also, be sure to credit your sources in comments for any code you adapt from elsewhere.

What to Hand In

Turn in a copy of your C source files using this online turnin form.

Hand in the following:

1. A printed copy of your C code.
2. A printout of a Unix session showing some sample input and the output of your programs given that input.