Assignment I Write seven small C programs

CS211 
Programming Assignment I

This assignment is designed to give you some initial experience with programming in C, as well
as compiling, running, and debugging. Your task is to write seven small C programs.
Section 1 describes the seven programs, section 2 describes how your project will be graded, and
section 3 describes how to structure and submit your project. In particular, section 3.1 describes
how to set up your project and provides an introduction to using the auto-grader. Please read the
entire assignment description before beginning the assignment.
Note that the assignment is due at 11:59 PM (ET). Submissions received after 11:59 PM
will not receive full credit, and no submission will be accepted more than six hours
past the deadline. You are strongly encouraged not to work until the last minute. Plan to submit
your assignment by October 12.
Advice Pay attention to the program descriptions, especially how the programs receive their input.
Some programs use only their command-line arguments (argv), others read from standard input
(with scanf() or similar), or from a file. Read the specifications carefully, and think about what is
being asked.
Make a plan before you start coding. If you cannot solve the problem yourself, you will not be
able to write a program to do it. Don’t be afraid to draw diagrams to guide your understanding of
the data structures or control flow.
If you have not used command-line shells before, be aware that the text you type at the prompt
is processed before being sent to a program as arguments. Most punctuation marks, aside from ., _,
and -, have special meanings and must be escaped or enclosed with quotation marks in order to pass
them to a program verbatim. You are not responsible for interpreting what the user typed: assume
that any strings your program receives are intentional and perform only the processing required by
the program specification.
Finally, it is not necessary to print a complete line at a time. If you are printing several strings
or other values sequentially, it is both simpler and more efficient to call printf multiple times than
to allocate a string, write the output to the string, and then print the string all at once. Similarly,
it is easier to read input one token at a time rather than reading a line and the breaking the line
into tokens.
1 Program descriptions
You will write six programs for this project. Except where explicitly noted, your programs may
assume that their inputs are properly formatted. However, your programs should be robust. Your
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program should not assume that it has received the proper number of arguments, for example, but
should check and report an error where appropriate.
Except where noted, programs should always terminate with exit code EXIT_SUCCESS (that is,
return 0 from main).
1.1 yell: String operations
Write a program yell that prints its argument all-caps. yell will read its first argument and print
it to standard output, replacing all lower-case characters with their corresponding upper-case letter.
After printing the modified string, it will print two exclamation points and a newline.
If the first argument to yell is an empty string, or if yell receives no arguments, it will print
nothing.
We will not test scenarios with more than one argument.
Usage
$ ./yell hello
HELLO!!
$ ./yell "I like NASA"
I LIKE NASA!!
$ ./yell
$ ./yell ""
$ ./yell " "
!!
The final three examples listed above demonstrate the behavior of yell when given (1) no
arguments, (2) an empty string, and (3) a string containing only a space.
Notes Use argc to determine the number of arguments. To check whether argv[1] is non-empty,
it is sufficient to check whether its first character is the terminator.
You may find the functions in ctype.h helpful. These include isupper, islower, toupper,
tolower, and more.
yell can be written without using malloc. Recall that output can be printed a single character
at a time, so it is not necessary to print the entire output at once.
1.2 rle: String operations II
Write a program rle that uses a simple method to compress strings. rle takes a single argument
and looks for repeated characters. Each repeated sequence of a letter or punctuation mark is reduced
to a single character plus an integer indicating the number of times it occurs. Thus, “aaa” becomes
“a3” and “ab” becomes “a1b1”.
If the compressed string is longer than the original string, rle must print the original string
instead.
If the input string contains digits, rle MUST print “error” and nothing else.
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Usage
$ ./rle aaaaaa
a6
$ ./rle aaabcccc..a
a3b1c4.2a1
$ ./rle aaabab
aaabab
$ ./rle a1b2
error
Notes Note that rle prints the original string if its compression method results in a larger string
than the input. Thus, in the third example above, it prints “aaabab” (length 6) and not “a3b1a1b1”
(length 8).
You MUST NOT assume that input strings have a maximum length. You will need to allocate
space to store the compressed string dynamically, based on the length of the input string. Given an
input string containing n characters, what is the maximum number of characters it a printed output
string? Is it necessary for rle to compress the entire input string before determining that it should
output the uncompressed string instead?
You MUST NOT assume any maximum number of times a character will be repeated. rle
should work equally well given a sequence of 10 or 1000 A’s. Rather than write your own integer to
string function, you can use sprintf or snprintf with an appropriate format string. Remember
that these functions work perfectly well when given a pointer to the middle of an allocated char
array, and will begin printing after that pointer. Both functions return the number of bytes witten,
which you can use to advance your pointer. (Read the manual and do some experiments to make
sure you account for terminator characters properly.)
1.3 balance: Strings and stacks
Write a program balance that checks whether a string contains correctly nested and balanced
parentheses, brackets, and braces. Your program will take a single argument and analyze whether
each open delimiter has a corresponding closing delimiter of the correct type.
If the string is balanced, balance will print nothing and exit with status EXIT_SUCCESS. Otherwise, balance will print an error message and exit with status EXIT_FAILURE.
Implementation balance will maintain a stack of open delimiters. Each time a (, [, or { is
encountered in the input, it will push that delimiter onto the stack. Each time a ), ], or } is
encountered, balance will pop the top delimiter off the stack and check whether it matches the
delimiter encountered in the string. If the delimiters do not match, or the stack is empty, balance
will print the index for the unexpected delimiter and the closing delimiter encountered.
$ ./balance ’)’
0: )
$ ./balance ’([)]’
2: )
If the stack is not empty when balance reaches the end of the input, it will print the message
open followed by a list of closing delimiters in the order needed to balance the string.
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$ ./balance ’([{’
open: }])
All non-delimiter characters may be ignored.
Notes You are free to use whatever data structures you find convenient. Note that an array can
be used to make a stack, if its size is bounded.
The optimal algorithm requires O(n) time and uses O(n) space, where n is the length of the
input string.
1.4 list: Linked lists
Write a program list that maintains and manipulates a sorted linked list according to instructions
received from standard input. The linked list is maintained in order, meaning that the items in the
list are stored in increasing numeric order after every operation.
Note that list will need to allocate space for new nodes as they are created, using malloc; any
allocated space should be deallocated using free as soon as it is no longer needed.
Note also that the list will not contain duplicate values.
list supports two operations:
insert n Adds an integer n to the list. If n is already present in the list, it does nothing. The
instruction format is an i followed by a space and an integer n.
delete n Removes an integer n from the list. If n is not present in the list, it does nothing. The
instruction format is a d followed by a space and an integer n.
After each command, list will print the length of the list followed by the contents of the list, in
order from first (least) to last (greatest).
list must halt once it reaches the end of standard input.
Input format Each line of the input contains an instruction. Each line begins with a letter (either
“i” or “d”), followed by a space, and then an integer. A line beginning with “i” indicates that the
integer should be inserted into the list. A line beginning with “d” indicates that the integer should
be deleted from the list.
Your program will not be tested with invalid input. You may choose to have list terminate in
response to invalid input.
Output format After performing each instruction, list will print a single line of text containing
the length of the list, a colon, and the elements of the list in order, all separated by spaces.
Usage Because list reads from standard input, you may test it by entering inputs line by line
from the terminal.
$ ./list
i 5
1 : 5
d 3
4
1 : 5
i 3
2 : 3 5
i 500
3 : 3 5 500
d 5
2 : 3 500
^D
To terminate your session, type Control-D at the beginning of the line. (This is indicated here by
the sequence ^D.) This closes the input stream to list, as though it had reached the end of a file.
Alternatively, you may use input redirection to send the contents of a file to list. For example,
assume list_commands.txt contains this text:
i 10
i 11
i 9
d 11
Then we may send this file to list as its input like so:
$ ./list < list_commands.txt
1 : 10
2 : 10 11
3 : 9 10 11
2 : 9 10
1.5 mexp: Matrix manipulation
Write a program mexp that multiplies a square matrix by itself a specified number of times. mexp
takes a single argument, which is the path to a file containing a square (k × k) matrix M and a
non-negative exponent n. It computes Mn and prints the result.
Note that the size of the matrix is not known statically. You must use malloc to allocate space
for the matrix once you obtain its size from the input file.
To compute Mn, it is sufficient to multiply M by itself n − 1 times. That is, M3 = M × M × M.
Naturally, a different strategy is needed for M0
.
Input format The first line of the input file contains an integer k. This indicates the size of the
matrix M, which has k rows and k columns.
The next k lines in the input file contain k integers. These indicate the content of M. Each line
corresponds to a row, beginning with the first (top) row.
The final line contains an integer n. This indicates the number of times M will be multiplied by
itself. n is guaranteed to be non-negative, but it may be 0.
For example, an input file file.txt containing
3
1 2 3
5
4 5 6
7 8 9
2
indicates that mexp must compute


1 2 3
4 5 6
7 8 9


2
.
Output format The output of mexp is the computed matrix Mn. Each row of Mn is printed on
a separate line, beginning with the first (top) row. The items within a row are separated by spaces.
Using file.txt from above,
$ ./mexp file1.txt
30 36 42
66 81 96
102 126 150
1.6 bst: Binary search trees
Write a program bst that manipulates binary search trees. It will receive commands from standard
input, and print resposes to those commands to standard output.
A binary search tree is a binary tree that stores integer values in its interior nodes. The value for
a particular node is greater than every value stored its left sub-tree and less than every value stored
in its right sub-tree. The tree will not contain any value more than once. bst will need to allocate
space for new nodes as they are created using malloc; any allocated space should be deallocated
using free before bst terminates.
This portion of the assignment has two parts.
Part 1 In this part, you will implement bst with three commands:
insert n Adds a value to the tree, if not already present. The new node will always be added as the
child of an existing node, or as the root. No existing node will change or move as as result of
inserting an item. If n was not present, and hence has been inserted, bst will print inserted.
Otherwise, it will print not inserted. The instruction format is an i followed by a decimal
integer n.
search n Searches the tree for a value n. If n is present, bst will print present. Otherwise, it will
print absent. The instruction format is an s followed by a space and an integer n.
print Prints the current tree structure, using the format in section 1.6.1.
Part 2 In this part, you will implement bst with an additional fourth command:
delete n Removes a value from the tree. See section 1.6.2 for further discussion of deleting nodes.
If n is not present, print absent. Otherwise, print deleted. The instruction format is a d
followed by a space and an integer n.
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Input format The input will be a series of lines, each beginning with a command character (i, s,
p, or d), possibly followed by a decimal integer. When the input ends, the program should terminate.
Your program will not be tested with invalid input. A line that cannot be interpreted may be
treated as the end of the input.
Output format The output will be a series of lines, each in response to an input command.
Most commands will respond with a word, aside from p. The format for printing is described in
section 1.6.1.
Usage
$ ./bst
i 1
inserted
i 2
inserted
i 1
not inserted
s 3
absent
p
(1(2))
^D
As with list, the ^D here indicates typing Control-D at the start of a line in order to signal the
end of file.
1.6.1 Printing nodes
An empty tree (that is, NULL) is printed as an empty string. A node is printed as a (, followed by
the left sub-tree, the item for that node, the right subtree, and ), without spaces.
For example, the output corresponding to fig. 1 is ((1)2((3(4))5(6))).
1.6.2 Deleting nodes
There are several strategies for deleting nodes in a binary tree. If a node has no children, it can
simply be removed. That is, the pointer to it can be changed to a NULL pointer. Figure 2a shows
the result of deleting 4 from the tree in fig. 1.
If a node has one child, it can be replaced by that child. Figure 2b shows the result of deleting 3
from the tree in fig. 1. Note that node 4 is now the child of node 5.
If a node has two children, its value will be changed to the maximum element in its left subtree.
The node which previously contained that value will then be deleted. Figure 2c shows the result of
deleting 5 from the tree in fig. 1. Note that the node that previously held 5 has been relabeled 4,
and that the previous node 4 has been deleted.
Note that the value being deleted may be on the root node.
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1
3
2
5
6
4
Figure 1: A binary search tree containing six nodes
1
3
2
5
6
(a) Deleted 4
1
4
2
5
6
(b) Deleted 3
1
3
2
4
6
(c) Deleted 5
Figure 2: The result of deleting different values from the tree in fig. 1
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2 Grading
Your submission will be awarded up to 100 points, based on how many test cases your programs
complete successfully.
The auto-grader provided for students includes half of the test cases that will be used during
grading. Thus, it will award up to 50 points.
Make sure that your programs meet the specifications given, even if no test case explicitly checks
it. It is advisable to perform additional tests of your own devising.
2.1 Academic integrity
You must submit your own work. You should not copy or even see code for this project written by
anyone else, nor should you look at code written for other classes. We will be using state of the art
plagiarism detectors. Projects which the detectors deem similar will be reported to the Office of
Student Conduct.
Do not post your code on-line or anywhere publically readable. If another student copies your
code and submits it, both of you will be reported.
3 Submission
Your solution to the assignment will be submitted through Sakai. You will submit a Tar archive
file containing the source code and makefiles for your project. Your archive should not include any
compiled code or object files.
The remainder of this section describes the directory structure (section 3.2), the requirements
for your makefiles (section 3.3), how to create the archive (section 3.4), and how to use the provided
auto-grader (section 3.5).
3.1 Getting started
Download the auto-grader and use tar to extract it. (The $ in these examples indicates a prompt.
The command you should type comes after the prompt and does not include the $.)
$ tar -xf pa1-grader.tar
This will create a directory pa1/, containing the auto-grader script and its associated data files.
First, create a subdirectory pa1/src/, which will contain a subdirectory for each of the six
programs (see section 3.2 for the suggested layout).
$ cd pa1
pa1$ mkdir src
(Here we are changing the prompt to indicate the working directory. As before, you only type
the text after the $.)
For each program, you will create a subdirectory with the same name as the program. It will
contain a makefile and the source code for your project. For example, to start work on yell, one
could create a directory yell inside pa1/src/ and copy the makefile template into it.
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pa1$ mkdir src/yell
pa1$ cp template.make src/yell/Makefile
The template is already set up for yell. For other programs, open the Makefile in the editor of
your choice and change the definition TARGET = yell so that TARGET is the name of that program.
Or, use sed to do the copy and edit in a single step.
pa1$ sed ’{s/yell/rle/;}’ template.make > src/rle/Makefile
Now create your source code. The template makefile assumes your code will be a single file with
the same name as the program. That is, the source for yell will be a file named yell.c in the
subdirectory src/yell. You are permitted to modify the makefile to use multiple source files or
different source file names, but take care to ensure compatibility with the auto-grader.
Once you have created your source file and are ready to compile, use the auto-grader to create
the build directory. This is where the auto-grader will place compiled programs and other files.
Using a separate build directory keeps your source directory free of clutter.
Running the auto-grader will create the build directory (if it does not exist), compile your
program, and run the provided test cases.
pa1$ ./grader.py
Alternatively, you may use the --init option to create the build directories without compiling
or running tests.
pa1$ ./grader.py --init
pa1$ cd build/yell
pa1/build/yell$ make
Because the build directory is created from your source code, you are always free to delete it and
have the auto-grader reconstruct it.
3.1.1 Testing early and often
The auto-grader provided to you is the same one we will use to test your code. To avoid disaster,
make sure that the auto-grader can compile and execute your program! Each time you make progress
with a program, run the auto-grader to check for improvement or regression.
By default, the auto-grader will test all the programs. If a list of programs or test groups is
provided, the auto-grader will perform only the specified tests. For example, to test only list, use:
pa1$ ./grader.py list
To get more information about failing test cases, use the --verbose or -v option, which will
print the full input to and output from the program on failing test cases. This may be combined
with the explicit list of tests to perform.
pa1$ ./grader.py -v
pa1$ ./grader.py -v list
Use -v twice to see input and output for successful test cases.
If the output from -v is overwhelming, use --stop or -1 to halt processing after the first failed
test case. (Note that --stop implies --verbose.)
pa1$ ./grader.py --stop
pa1$ ./grader.py -1 bst:2
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3.2 Directory structure
Your project should be stored in a directory named src, which will contain three sub-directories.
Each subdirectory will have the name of a particular program, and contain (1) a makefile, and (2)
any source files needed to compile your program. Typically, you will provide a single C file named
for the program. That is, the source code for the program factor would be a file factor.c, located
in the directory src/factor.
This diagram shows the layout of a typical project:
src
+- yell
| +- Makefile
| +- yell.c
+- rle
| +- Makefile
| +- rle.c
+- balance
| +- Makefile
| +- balance.c
+- list
| +- Makefile
| +- list.c
+- mexp
| +- Makefile
| +- mexp.c
+- bst
+- Makefile
+- bst.c
3.3 Makefiles
We will use make to manage compilation. Each program directory will contain a file named Makefile
that describes at least two targets. The first target must compile the program. An additional
target, clean, must delete any files created when compiling the program (typically just the compiled
program).
The auto-grader script is distributed with an example makefile, which looks like this (note that
an actual makefile must use tabs rather than spaces for indentation):
TARGET = yell
CC = gcc
CFLAGS = -g -std=c99 -Wall -Wvla -Werror -fsanitize=address,undefined
$(TARGET): $(TARGET).c
$(CC) $(CFLAGS) $^ -o $@
clean:
rm -rf $(TARGET) *.o *.a *.dylib *.dSYM
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It is simplest to copy this file into the directories for each program, replacing yell with the name
of that specific program. This will ensure that you programs will be compiled with the recommended
options.
It is further recommended that you use make to compile your programs, rather than invoking the
compiler directly. This will ensure that your personal testing is performed with the same compiler
settings as the auto-grader. The makefiles created in the build directory by the auto-grader refer to
the makefiles you create in the source directory and therefore pick up any changes made.
You may add additional compiler options as you see fit, but you are advised to leave the compiler
warnings, sanitizers, and debugger information (-g). The makefile shown here specifies the C99
standard, in order to allow C++-style // comments; you may change that to C89, if you prefer.
Compiler options The sample makefile uses the following compiler options, listed in the CFLAGS
make variable:
-g Include debugger information, used by GDB and AddressSanitizer.
-std=c99 Require conformance with the 1999 C Standard. (Disable GCC extensions.) You may
change this to -std=c89 or -std=c90 at you discretion.
-Wall Display most common warning messages.
-Wvla Warn when using variable-length arrays.
-Werror Promote all warnings to errors.
-fsanitize=address,undefined Include run-time checks provided by AddressSanitizer and UBSan.
This will add code that detects many memory errors and guards against undefined behavior.
(Note that these checks discover problems with your code. Disabling them will not make your
code correct, even if it seems to execute correctly.)
Target and dependency variables Note the use of $@ (indicating the target name) and $^
(indicating the dependencies). The auto-grader uses some advanced features of make to put the
source files and object files in different directories. If you prefer to write your own Makefile, you
will need to use these variables in order for the auto-grader to successfully compile your project.
Contact me with any questions about how to do this.
3.4 Creating the archive
We will use tar to create the archive file. To create the archive, first ensure that your src directory
contains only the source code and makefiles needed to compile your project. Any compiled programs,
object files, or other additional files should be moved or removed.
Next, move to the directory containing src and execute this command:
pa1$ tar -vzcf pa1.tar src
tar will create a file pa1.tar that contains all files in the directory src. This file can now be
submitted through Sakai.
To verify that the archive contains the necessary files, you can print a list of the files contained
in the archive with this command:
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pa1$ tar -tf pa1.tar
You should also use the auto-grader to confirm that your archive is correctly structured.
pa1$ ./grader.py -a pa1.tar
3.5 Using the auto-grader
We have provided a tool for checking the correctness of your project. The auto-grader will compile
your programs and execute them several times with different arguments, comparing the results
against the expected results.
Setup The auto-grader is distributed as an archive file pa1-grader.tar. To unpack the archive,
move the archive to a directory and use this command:
pa1$ tar -xf pa1-grader.tar
This will create a directory pa1 containing the auto-grader itself, grader.py, a library autograde.py,
and a directory of test cases data.
Do not modify any of the files provided by the auto-grader. Doing so may prevent the auto-grader
from correctly assessing your program.
You may create your src directory inside pa1. If you prefer to create src outside the pa1
directory, you will need to provide a path to grader.py when invoking the auto-grader (see below).
Usage While in the same directory as grader.py and src, use this command:
pa1$ ./grader.py
The auto-grader will compile and execute the programs in the directory src, assuming src has the
structure described in section 3.2.
By default, the auto-grader will attempt to grade all programs. You may also provide one or
more specific programs to grade. For example, to grade only rle:
pa1$ ./grader.py rle
To stop the auto-grader after the first failed test case, use the --stop or -1 option.
To obtain usage information, use the -h option.
Program output By default, the auto-grader will not print the output from your programs,
except for lines that are incorrect. To see all program output for unsuccessful tests, use the
--verbose or -v option:
pa1$ ./grader.py -v
To see program output for all tests, use -vv. To see no program output, use --quiet or -q.
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Checking your archive We recommend that you use the auto-grader to check an archive
before submitting. To do this, use the --archive or -a option with the archive file name. For
example,
pa1$ ./grader.py -a pa1.tar
This will unpack the archive into a temporary directory, grade the programs, and then delete the
temporary directory.
Specifying source directory If your src directory is not located in the same directory as
grader.py, you may specify it using the --src or -s option. For example,
pa1$ ./grader.py -s ../path/to/src
Refreshing the build directory In the unlikely event that your build directory has become
corrupt or otherwise unusable, you can simply delete it using rm -r build. Alternatively, the
--fresh or -f option will delete and recreate the build directory before testing.
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