CSE 413 Autumn 2007

Assignment 4 - C Warmup

Due: Electronically: 8am Friday, October 26, 2007. On paper: Printout showing test cases due at the beginning of class on Friday, October 26, 2007.

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 fgets 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. In particular, some of the functions in stdio.h, string.h, and ctype.h may be useful. Refer to Section 7 in the Essential C guide posted on our C references page. Be sure to #include any libraries you use at the top of your program.
• 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 (one source file for part 1, one source file for part 2); 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 in general are not good style. For part 1 it will be o.k. if you have everything in main. For part 2 you should write at least one function other than main.

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.

What to Hand In

Turn in a copy of your C source files using this link.

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.