Programming Assignment #3: ListyFib
In this programming assignment, you will implement a Fibonacci function that
avoids repetitive computation by computing the sequence linearly from the
bottom up: F(0) through F(n). You will also overcome the limitations of C’s 32-
bit integers by storing very large integers in linked lists with nodes that contain
By completing this assignment, you will gain experience crafting algorithms of
moderate complexity, develop a deeper understanding of integer type
limitations, become better acquainted with unsigned integers, and reinforce your
understanding of dynamic memory management in C. You will also master the
craft of linked list manipulation! In the end, you will have a very fast and
awesome program for computing huge Fibonacci numbers.
Important note: In your assignments, you can use any code I’ve posted in
Webcourses, as long as you leave a comment saying where the code came from.
However, you cannot use code posted by other professors, and you should never
incorporate or refer to code from online resources or from other individuals. Of
course, you will learn more if you try to implement everything from scratch
without copying any of my code from Webcourses.
Note! The capitalization and spelling of your filename matter!
Note! Code must be tested on Eustis, but submitted via Webcourses.
1.1. Computational Considerations for Recursive Fibonacci
We’ve seen in class that calculating Fibonacci numbers with the most straightforward recursive implementation
of the function is prohibitively slow, as there is a lot of repetitive computation:
int fib(int n)
// base cases: F(0) = 0, F(1) = 1
if (n < 2)
// definition of Fibonacci: F(n) = F(n – 1) + F(n – 2) for n 1
return fib(n – 1) + fib(n – 2);
This recursive function sports an exponential runtime. We saw in class that we can achieve linear runtime by
building from our base cases, F(0) = 0 and F(1) = 1, toward our desired result, F(n). We thus avoid our expensive
and exponentially EXplOsIVe recursive function calls.
The former approach is called “top-down” processing, because we work from n down toward our base cases.
The latter approach is called “bottom-up” processing, because we build from our base cases up toward our
desired result, F(n). In general, the process by which we eliminate repetitive recursive calls by re-ordering our
computation is called “dynamic programming,” and is a topic we will explore in more depth in COP 3503
(Computer Science II).
1.2. Representing Huge Integers in C
Our linear Fibonacci function has a big problem, though, which is perhaps less obvious than the original runtime
issue: when computing the sequence, we quickly exceed the limits of C’s 32-bit integer representation. On most
modern systems, the maximum int value in C is 231-1, or 2,147,483,647.1
The first Fibonacci number to exceed
that limit is F(47) = 2,971,215,073.
Even C’s 64-bit unsigned long long int type is only guaranteed to represent non-negative integers up to and
including 18,446,744,073,709,551,615 (which is 264-1).2 F(93) is 12,200,160,415,121,876,738, which can be
stored as an unsigned long long int. However, F(94) is 19,740,274,219,868,223,167, which is too big to store in
any of C’s extended integer data types.
To overcome this limitation, we will represent integers in this program using linked lists, where each node holds
a single digit of an integer.3
For reasons that will soon become apparent, we will store our integers in reverse
1 To see the upper limit of the int data type on your system, #include <limits.h, and then printf(“%d\n”, INT_MAX);
2 To see the upper limit of the unsigned long long int data type on your system, #include <limits.h, and then
3 Admittedly, there is a lot of wasted space with this approach. We only need 4 bits to represent all the digits in the range 0
through 9, yet the int type on most modern systems is 32 bits. Thus, we’re wasting 28 bits for every digit in the huge
integers we want to represent (not to mention the space taken up by all those nodes’ next pointers)! Even C’s smallest
data type utilizes at least one byte (8 bits), giving us at least 4 bits of unnecessary overhead.
order in these linked lists. So, for example, the numbers 2,147,483,648 and 100,087 would be represented as:
Storing these integers in reverse order makes it much easier to add two of them together than if we stored them
the other way around. The ones digit for each integer is stored in the first node in its respective linked list, the
tens digit is stored in the second node, the hundreds digit is stored in the third node, and so on. How convenient!
So, to add these two numbers together, we add the values in the first nodes (8 + 7 = 15), throw down the 5 in the
first node of some new linked list where we want to store the sum, carry the 1, add it to the values in the second
nodes of our linked lists (1 + 4 + 8 = 13), and so on:
In this program, we will use this linked list representation for integers. The nodes will of course be allocated
dynamically, and we will stuff the head of each linked list inside a struct that also keeps track of the list’s length:
typedef struct ListyInt
// The head of a linked list that holds the digits
// of an integer, stored in reverse order.
// The number of digits in the integer (which is
// equal to the number of nodes in the list).
This struct is defined in ListyFib.h. There is, of course, a corresponding node struct defined in ListyFib.h, as
a: 8 4 6 3 8 4 7 4 1 2 (NULL)
b: 7 8 0 0 0 1 (NULL)
8 4 6 3 8 4 7 4 1 2
7 8 0 0 0 1
5 3 7 3 8 5 7 4 1 2
0 0 0 0
+ + + + + + + + + +
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
1.3. ListyFib.h (Super Important!)
For your linked lists, you must use the ListyInt and Node structs we have specified in ListyFib.h without any
modifications. Do not add those struct definitions to your code, though. Instead, you must #include the header
file that contains those struct definitions by adding the following line of code to your ListyFib.c source file:
1.4. Unsigned Integers and limits.h
There’s one final curve ball you have to deal with: there are a few places where your program will utilize
unsigned integers. This is no cause to panic. An unsigned integer is just an integer that can’t be negative.
(There’s no “sign” associated with the value. It’s always non-negative.) As we’ve seen in class, you declare an
unsigned integer like so:
unsigned int n;
Because an unsigned int is typically 32 bits (like the normal int data type), but doesn’t need to use any of those
bits to signify a sign, it can eke out a higher maximum positive integer value than a normal int.
For at least one function in this assignment, you’ll need to know what the maximum value is that you can
represent using an unsigned int on the system where your program is running. That value is defined in your
system’s limits.h file, which you should #include from your ListyFib.c source file, like so:
limits.h defines a value called UINT_MAX, which is the maximum value an unsigned int can hold. It also defines
INT_MAX (the maximum value an int can hold), UINT_MIN, INT_MIN, and many others that you might want to
read up on in your spare time.
If you want to print an unsigned int, the correct conversion code is %u. For example:
unsigned int n = UINT_MAX;
printf(“Max unsigned int value: %u\n”, n);
Note that (UINT_MAX + 1) necessarily causes integer overflow, but since an unsigned int can’t be negative,
(UINT_MAX + 1) just wraps back around to zero. Try this out for fun:4
unsigned int n = UINT_MAX;
printf(“Max unsigned int value (+1): %u\n”, n + 1);
Compare this, for example, to the integer overflow caused by the following:
int n = INT_MAX;
printf(“Max int value (+1): %d\n”, n + 1);
4 Here, “fun” is a relative term.
2. Function Requirements
In the source file you submit, ListyFib.c, you must implement the following functions. You may implement any
auxiliary functions you need to make these work, as well. Note that none of your functions should print to the
screen, and the file you submit should not have a main() function.
ListyInt *listyAdd(ListyInt *p, ListyInt *q);
Description: Return a pointer to a new, dynamically allocated ListyInt struct that contains the result of
adding the integers represented by p and q.
Special Notes: If a NULL pointer is passed to this function, simply return NULL. If any dynamic
memory allocation functions fail within this function, also return NULL, but be careful to avoid memory
leaks when you do so.
Another Special Note: If an argument passed to this function is non-NULL, you can assume that the
head pointer inside that struct is also non-NULL and that the length is greater than zero. You may also
assume that any non-NULL ListyInt struct passed to the functions in this assignment will be wellformed. For example, if the length field of a ListyInt is set to 3, the list will have exactly three nodes, and
the last node’s next pointer will be set to NULL.
Runtime Restriction: The runtime of this function must be no worse than O(m + n), where m is the
length of p, and n is the length of q.
Returns: A pointer to the newly allocated ListyInt struct, or NULL in the special cases mentioned above.
ListyInt *destroyListyInt(ListyInt *listy);
Description: Destroy any and all dynamically allocated memory associated with listy in O(n) time
(where n is the length of the list). Avoid segmentation faults and memory leaks.
ListyInt *stringToListyInt(char *str);
Description: Convert a number from string format to ListyInt format in O(k) time (where k is the length
of str). (For example function calls, see testcase01.c)
Special Notes: If the empty string (“”) is passed to this function, treat it as a zero (“0”). If any dynamic
memory allocation functions fail within this function, or if str is NULL, return NULL, but be careful to
avoid memory leaks when you do so. You may assume the string will only contain ASCII digits ‘0’
through ‘9’, and that there will be no leading zeros in the string.
Returns: A pointer to the newly allocated ListyInt struct, or NULL if dynamic memory allocation fails
or if str is NULL.
Continued on the following page…
char *listyIntToString(ListyInt *listy);
Description: Convert the integer represented by listy to a dynamically allocated string, and return a
pointer to that string (i.e., return the base address of the char array). Be sure to properly terminate the
string with a null sentinel (‘\0’). If listy is NULL, or if any calls to malloc() fail, simply return NULL.
The runtime for this function must not exceed O(n) (where n is the length of the list).
Returns: A pointer to the dynamically allocated string, or NULL if dynamic memory allocation fails at
any point or if listy is NULL.
ListyInt *uintToListyInt(unsigned int n);
Description: Convert the unsigned integer n to ListyInt format. If any dynamic memory allocation
functions fail within this function, return NULL, but be careful to avoid memory leaks when you do so.
Your runtime for this function cannot exceed O(k), where k is the number of digits in n.
Returns: A pointer to the newly allocated ListyInt struct, or NULL if dynamic memory allocation fails at
unsigned int *listyIntToUint(ListyInt *listy);
Description: Convert the integer represented by listy to a dynamically allocated unsigned int, and return
a pointer to that value. If listy is NULL, simply return NULL. If the integer represented by listy exceeds
the maximum unsigned int value defined in limits.h, return NULL.
Note: The sole reason this function returns a pointer instead of an unsigned int is so that we can return
NULL to signify failure in cases where listy cannot be represented as an unsigned int.
Returns: A pointer to the dynamically allocated unsigned integer, or NULL if the value cannot be
represented as an unsigned integer (including the case where listy is NULL).
void plusPlus(ListyInt *listy);
Description: Increment the value held in listy by one. If listy is NULL, simply return. You don’t
necessarily have to use this function anywhere else in your program. It’s just here as an additional
Special Note: If any dynamic memory allocation functions fail within this function, simply leave the
value in listy unmodified. (Such a failure is unlikely anyway, and will not be explicitly tested for this
Returns: Nothing. This is a void function.
ListyInt *fib(unsigned int n);
Description: This is your Fibonacci function. This is where the magic happens. Implement an iterative
solution that runs in O(nk) time and returns a pointer to a ListyInt struct that contains F(n). (See runtime
note below.) Be sure to prevent memory leaks before returning from this function.
Runtime Consideration: In the O(nk) runtime restriction, n is the parameter passed to the function, and
k is the number of digits in F(n). So, within this function, you can make O(n) number of calls to any
function that is O(k) (or faster).
Space Consideration: When computing F(n) for large n, it’s important to keep as few Fibonacci
numbers in memory as necessary at any given time. For example, in building up to F(10000), you won’t
want to hold Fibonacci numbers F(0) through F(9999) in memory all at once. Find a way to have only a
few Fibonacci numbers in memory at any given time over the course of a single call to to fib().
Special Notes: Notice that n will always be a non-negative integer. If any dynamic memory allocation
functions fail within this function, return NULL, but be careful to avoid memory leaks when you do so.
Returns: A pointer to a ListyInt representing F(n), or NULL if dynamic memory allocation fails.
Description: Returns a double indicating how difficult you found this assignment on a scale of 1.0
(ridiculously easy) through 5.0 (insanely difficult).
Description: Returns a reasonable and realistic estimate (greater than zero) of the number of hours you
spent on this assignment.
3. Running All Test Cases on Eustis (test-all.sh)
The test cases included with this assignment are designed to show you some ways in which we might test your
code and to shed light on the expected functionality of your code. We’ve also included a script, test-all.sh, that
will compile and run all test cases for you.
Super Important: Using the test-all.sh script to test your code on Eustis is the safest, most sure-fire way to make
sure your code is working properly before submitting.
To run test-all.sh on Eustis, first transfer it to Eustis in a folder with ListyFib.c, ListyFib.h, all the test case files,
and the sample_output directory. Transferring all your files to Eustis with MobaXTerm is fairly straightforward,
but if you want to transfer them from a Linux or Mac command line, here’s how you do it:
1. At your command line on your own system, use cd to go to the folder that contains all your files for this
project (ListyFib.c, ListyFib.h, all the test case files, and the sample_output folder).
2. From that directory, type the following command (replacing YOUR_NID with your actual NID) to transfer
that whole folder to Eustis:
scp -r $(pwd) [email protected]:~
Warning: Note that the $(pwd) in the command above refers to your current directory when you’re at the
command line in Linux or Mac OS. The command above transfers the entire contents of your current
directory to Eustis. That will include all subdirectories, so for the love of all that is good, please don’t run
that command from your desktop folder if you have a ton of files on your desktop!
Once you have all your files on Eustis, you can run test-all.sh by connecting to Eustis and typing the following:
If you put those files in their own folder on Eustis, you will first have to cd into that directory. For example:
That command (bash test-all.sh) will also work on Linux systems and with the bash shell for Windows. It will
not work at the Windows Command Prompt, and it might have limited functionality in Mac OS.
Warning: When working at the command line, any spaces in file names or directory names either need to be
escaped in the commands you type (cd project\ 3), or the entire name needs to be wrapped in double quotes.
4. Running the Provided Test Cases Individually
If the test-all.sh script is telling you that some of your test cases are failing, you’ll want to compile and run those
test cases individually to inspect their output. Here’s how to do that:
1. Place all the test case files released with this assignment in one folder, along with your ListyFib.c file.
2. At the command line, cd to the directory with all your files for this assignment, and compile your source
file with one of our test cases (such as testcase01.c) like so:
gcc ListyFib.c testcase01.c
3. To run your program and redirect the output to output.txt, execute the following command:
4. Use diff to compare your output to the expected (correct) output for the program:
diff output.txt sample_output/testcase01-output.txt
If the files differ, diff will spit out some information about the lines that aren’t the same. For example:
[email protected]:~$ diff output.txt sample_output/testcase01-output.txt
< F(5) = 3
F(5) = 5
[email protected]:~$ _
If the contents of output.txt and testcase01-output.txt are exactly the same, diff won’t have any output:
[email protected]:~$ diff output.txt sample_output/testcase01-output.txt
[email protected]:~$ _
Super Important: Remember, using the test-all.sh script to test your code on Eustis is the safest, most sure-fire
way to make sure your code is working properly before submitting.
5. Testing for Memory Leaks with Valgrind
Part of the credit for this assignment will be awarded based on your ability to implement the program without
any memory leaks. To test for memory leaks, you can use a program called valgrind, which is installed on
Valgrind will not guarantee that your code is completely free of memory leaks. It will only detect whether any
memory leaks occur when you run your program. So, if you have a function called foo() that has a nasty memory
leak, but you run your program in such a way that foo() never gets called, valgrind won’t be able to find that
potential memory leak.
The test-all.sh script will automatically run your program through all test cases and use valgrind to check
whether any of them result in memory leaks. If you want to run valgrind manually, simply compile your program
with the -g flag, and then run it through valgrind, like so:
gcc ListyFib.c testcase01.c -g
valgrind –leak-check=yes ./a.out
In the output of valgrind, the magic phrase you’re looking for to indicate that no memory leaks were detected is:
All heap blocks were freed — no leaks are possible
For more information about valgrind’s output, see: http://valgrind.org/docs/manual/quick-start.html
6. Special Restrictions (Super Important!)
You must abide by the following restrictions in the ListyFib.c file you submit. Failure to abide by any one of
these restrictions could result in a catastrophic loss of points.
Do not read or write to files (using, e.g., C’s fopen(), fprintf(), or fscanf() functions). Also, please do not
use scanf() to read input from the keyboard.
Do not declare new variables part way through a function. All variable declarations should occur at the
top of a function, and all variables must be declared inside your functions or declared as function
Do not use goto statements in your code.
Do not make calls to C’s system() function.
Do not write malicious code, including code that attempts to open files it shouldn’t be opening, whether
for reading or writing. (I would hope this would go without saying.)
No crazy shenanigans.
7. Style Restrictions (Super Important!)
Please conform as closely as possible to the style I use while coding in class. To encourage everyone to develop
a commitment to writing consistent and readable code, the following restrictions will be strictly enforced:
Any time you open a curly brace, that curly brace should start on a new line.
Any time you open a new code block, indent all the code within that code block one level deeper than
you were already indenting.
Be consistent with the amount of indentation you’re using, and be consistent in using either spaces or tabs
for indentation throughout your source file. If you’re using spaces for indentation, please use at least two
spaces for each new level of indentation, because trying to read code that uses just a single space for each
level of indentation is downright painful.
Please avoid block-style comments: /* comment */
Instead, please use inline-style comments: // comment
Always include a space after the “//” in your comments: “// comment” instead of “//comment”
The header comments introducing your source file (including the comment(s) with your name, course
number, semester, NID, and so on), should always be placed above your #include statements.
Use end-of-line comments sparingly. Comments longer than three words should always be placed above
the lines of code to which they refer. Furthermore, such comments should be indented to properly align
with the code to which they refer. For example, if line 16 of your code is indented with two tabs, and line
15 contains a comment referring to line 16, then line 15 should also be intended with two tabs.
Please do not write excessively long lines of code. Lines must be no longer than 100 characters wide.
Avoid excessive consecutive blank lines. In general, you should never have more than one or two
consecutive blank lines.
When defining a function that doesn’t take any arguments, always put void in its parentheses. For
example, define a function using int do_something(void) instead of int do_something().
When defining or calling a function, do not leave a space before its opening parenthesis. For example:
use int main(int argc, char **argv) instead of int main (int argc, char **argv). Similarly, use printf(“…”)
instead of printf (“…”).
Do leave a space before the opening parenthesis in an if statement or a loop. For example, use
use for (i = 0; i < n; i++) instead of for(i = 0; i < n; i++), and use if (condition) instead of if(condition)
or if( condition ).
Please leave a space on both sides of any binary operators you use in your code (i.e., operators that take
two operands). For example, use (a + b) – c instead of (a+b)-c. (The only place you do not have to follow
this restriction is within the square brackets used to access an array index, as in: array[i+j].)
Use meaningful variable names that convey the purpose of your variables. It’s fine to use single-letter
variable names for short functions (e.g., a simple max function, such as int max(int a, int b), where it
would be silly to try to come up with more meaningful variable names for those two input parameters),
for control variables in your for loops (where i, j, and k are common variable name choices), or for sizes
and lengths of certain inputs (e.g., using n for the length of an array). Otherwise, please try to use variable
names that convey the intended use of your variables. Names like cheeseburger and pizza are not good
choices for this particular program.
Submit a single source file, named ListyFib.c, via Webcourses. The source file should contain definitions for all
the required functions (listed above), as well as any auxiliary functions you need to make them work. Be sure to
include your name and NID in a header comment at the top of your source file. Also, don’t forget to #include
“ListyFib.h” in your source code (with correct capitalization).
Do not submit additional source files, do not submit a modified ListyFib.h header file, and do not include a
main() function in your ListyFib.c source file. Your source file must work with the test-all.sh script, and it must
also compile on Eustis in both of the following ways:
gcc -c ListyFib.c
gcc ListyFib.c testcase01.c
Important Note: When grading your programs, we will use different test cases from the ones we’ve released
with this assignment, to ensure that no one can game the system and earn credit by simply hard-coding the
expected output for the test cases we’ve released to you. You should create additional test cases of your own
in order to thoroughly test your code. In creating your own test cases, you should always ask yourself, “How
could these functions be called in ways that don’t violate the function descriptions, but which haven’t already
been covered in the test cases included with the assignment?”
The tentative scoring breakdown (not set in stone) for this programming assignment is:
60% Passes test cases with 100% correct output formatting.
20% Passes valgrind test cases (no memory leaks).
10% Implementation details and adherence to the special restrictions imposed on this assignment.
This will likely involve some manual inspection of your code.
10% Follows all style restrictions; has adequate comments and whitespace; source file is named
correctly and includes your name and NID (not your UCF ID) in a header comment. We will
likely impose huge penalties for small deviations from style restrictions because we really
want you to develop good style habits in this class.
Note! Your program must be submitted via Webcourses, and it must compile and run on Eustis to receive credit.
Programs that do not compile will receive an automatic zero.
Your grade will be based largely on your program’s ability to compile and produce the exact output expected.
Even minor deviations (such as capitalization or punctuation errors) in your output will cause your program’s
output to be marked as incorrect, resulting in severe point deductions. The same is true of how you name your
functions and their parameters. Please be sure to follow all requirements carefully and test your program
throughly. Your best bet is to submit your program in advance of the deadline, then download the source code
from Webcourses, re-compile, and re-test your code in order to ensure that you uploaded the correct version of
your source code.
Additional points may be awarded for style (proper commenting and whitespace) and adherence to
implementation requirements. For example, the graders might inspect your listyAdd() function to see that it
handles malloc() failures properly.
Please note that you will not receive credit for test cases that call your Fibonacci function if that function’s
runtime is worse than O(nk), or if your program has memory leaks that slow down execution. In grading,
programs that take longer than a fraction of a second per test case (or perhaps a whole second or two for very
large test cases) will be terminated. That won’t be enough time for a traditional recursive implementation of the
Fibonacci function to compute results for the large values of n that we will pass to your programs.
Start early. Work hard. Good luck!