CSE 303, Winter 2007, Assignment 3

Due: Wednesday, January 31 2007, 6:00pm

Assignment goal

You will get experience writing short C programs and manipulating strings and arrays in C.

Documentation

In addition to the lecture notes, you may find "Programming in C" a useful reference for completing this assignment.

Getting ready

Download the file: hw3.tar.gz.

Extract all the files for this assignment using the following command:

> tar zxvf hw3.tar.gz

You should now see a directory called hw3.

If you see it, you are ready to start the assignment. If this procedure did not work for you, please contact a TA or talk to another student in the class.

1. Warm-up

Every time you learn a new language, the first thing you need to try is to write the simplest program possible.

In a file called my_test.c, write a C program that prints the string "Success!" and exits.

In a file called my_test2.c, write a C program that takes two integers as command line arguments and outputs their sum. This program does not have to perform any error-checking, except to check that the correct number of arguments is provided. If the user provides fewer than 2 arguments on the command line, your program should print an error message and should exit with exit status 1.

Hint: To convert a string to an integer, one possibility is to use the atoi function. To learn more about this function try man atoi or use your book.

2. Formatted Input/Output

In a file called problem2.c, write a C program that prompts the user for a floating point number and prints the following:

• The floating point number with exactly two decimal points.
• The floating point number in exponential notation with exactly two decimal points.

Requirement: The results should appear on two distinct lines and should look right-aligned with respect to each other.

Example:

./problem2

Please enter a floating point number: > 45.6

3. Arrays and pointers

Examine the file problem3.c. It contains three functions in addition to main. Each function corresponds to one question. Each question asks you to either complete or explain the code.

Please complete problem3.c by adding the missing code and answering the questions directly in the file.

To answer a question, uncomment the call to the corresponding function in main. Compile and execute the program problem3.c. Examine the output produced.

4. Arrays

In a file called problem4.c, write a C program that takes a list of N integers as command line arguments and performs the following operations:

• Prints the average value
• Prints the minimum and maximum values
• Prints the numbers in the following order: all the odd numbers appear first in increasing order, then all the even numbers in increasing order.

Requirement: You program must be composed of at least five functions.

• The function main should perform all the input and output operations. It should read the list of integers given as argument. It should output the results. No other function is allowed to write anything to stdout.
• A helper function average should compute the average value of all the integers. The function average should have the following prototype: int average(int numbers[], int size)
  where,
  • numbers is an array of integers
  • size is the size of the array
  • the returned value is the average
• A helper function min_max should compute the minimum and maximum values found in the array. The function min_max should have the following prototype: void min_max(int *numbers, int size, int *min, int *max). Note: We ask you to use int *numbers instead of int numbers[] to show you that they are equivalent.
• A helper function less_than should take two numbers as argument and return true if the first one precedes the second one in the order defined above, and false otherwise.
• A helper function sort should sort the list of integers in the required order. Your sort function need not be efficient. The function sort should have the following prototype: void sort(int numbers[], int size), and it should use the less_than function.

Requirement 2: All functions should be preceded by a comment block of the following form. For each parameter, indicate in the description whether it is modified by the function or not.

/**
* Brief description of the function
* @param name_of_first_param description of first param
* @param name_of_second_param description of second param
* @return description of what value is returned
*/

5. Strings

Your friend Bob is just learning about strings in C. He is having a lot of trouble. He wrote a few functions in a file called problem5.c, but some of them have bugs and some of them are not complete. Can you help him finish his work?

Hints:

• Uncomment and fix or complete only one of the string_exampleX() functions at the time.
• If the program crashes, you may find gdb useful for finding the location of the crash. Beware that some bugs cause programs to crash sometime *after* a buggy statement. Also remember to compile the program with option -g.
• Pages 470 and 471 in the book describe the string functions available in the standard library ( problem5.c uses several of these functions).

6. Extra-Credit

Note: this problem is not especially hard. If you have time to do it, you should try. It will give you additional practice working with strings.

In a file called problem6.c, write a C program that takes a list of N strings as input (on the command line) and performs the following actions:

• For each string, if the string contains the letter 's', it writes a '\0' at that location in the string. If the string does not contain the letter 's', nothing happens.
• Reverses each string. For example, string "hello" will become "olleh"
• Given the modified list of strings, the program prints the strings in increasing alphabetical order, with one string per line. For each string, the program also outputs the new length of the string.
• The output is formatted such that the string names and string sizes appear in two columns (Note: pick an arbitrary fixed size for the columns and don't worry about strings that are too long).
• N can be arbitrarily high (i.e., you cannot assume any particular fixed bound).

Here's a sample output:

./problem6 boston laptop yesterday geese sweden book

Requirement2: Make sure to comment all the functions that you write, using the same style of comments as in the previous question.

Turn-in instructions

You should work on this assignment in a group of two. Each group should turn-in only one copy of the solution. Please make sure to write both names inside each file that you hand in.

Here is the list of files that you need to turn in:

• Problem 1: my-test.c and my-test2.c
• Problem 2: problem2.c
• Problem 3: problem3.c
• Problem 4: problem4.c
• Problem 5: problem5.c
• Extra-Credit: problem6.c

Please find the detailed turn-in instructions here.