Project 1: List Abstract Data Type (ADT)

In this project, you (and at most one partner) will be required to implement a List ADT in two ways. You will implement the List ADT using arrays, and using linked lists.

Important Updates

  • Your initial array size may not exceed 32 entries (realloc must be called at least once to store 33 items).
  • You may not use static or global variables. Any state that you need to maintain persistance for is available through the proper struct List.
  • Even though there isn’t a test for it, you must check to ensure all memory allocations succeed. If a memory allocation fails you must handle it gracefully as indicated by the function.

Goals for this project

By the time you have completed this project, you should:

  • understand what an abstract data type is
  • understand how the concept of separate compilation works (.h and .c files) – review the separate compilation example if necessary
  • become familiar with working with linked structures (necessary for the remainder of this class)
  • be able to discuss the trade-offs in performance between an array-based implementation and a linked-list implementation of the List ADT

Project Preparation

Before you begin, let’s prepare a cs24 directory in your home directory if you don’t already have one. In that directory we’ll create a subdirectory for the files for this project. Note that these instructions assume you are using either a CSIL machine or one of the lab machines:

After logging in, create the directory (assuming you haven’t already done so):

mkdir -p cs24/proj1

Change the permissions of the cs24 directory such that only your account can access the files inside this directory. This step is incredibly important. If omitted, other students can peek at your work and you may be held partially responsible. It should also go without saying that you may not give other students access to your account. If you’ve done that in the past please change your password at this time.

chmod 700 cs24

Change into the proj1 directory and copy the files you will need for this project:

cd cs24/proj1
cp ~bboe/public_html/cs24_f13/code/proj1/* .

The provided files

You are provided with the following files:

  • list.h: This file provides the interface to the List ADT. You may not modify this file, thus you must work with the List structure as provided. This file provides the declarations for all the functions you must implement. The comments in this file indicate exactly how each function should perform. Read this entire file and understand it. Pay particular attention to how we can easily switch between using the array-based implementation and the linked-implementation by using MACRO-conditionals around the structure declaration(s).

  • main.c: This is a complete example program that can be used to test your implementations of the List ADT. While you do not need to modify this file, you are expected to understand 100% of the code in it.

  • Makefile: If you haven’t seen a makefile before, this is a special file that contains the command-line arguments required to build the project. By executing make in the terminal you will see the list of available make options. When working on the array-based implementation you will likely want to run make array and make test_array. For the link-based implementation make linked and make test_linked.

  • test_list.c: This program provides unit-like testing of individual functions and has been provided to you as a convenience. You are not expected to know exactly how the code in this program works (it makes use of passing function pointers around). The submission system uses a version of this file that defines many more tests (NOTE: the test numbers do not correspond between the submission system and the numbers in this file). You are encouraged to add your own tests to this file to help you test your program without the help of the submission system. To add a test you need to (1) define a function that takes a struct List * as its only argument, and returns an integer, 0 for failure and non-zero for success. You then (2) need to add the name of the function, and an output name to the TESTS array.

Completing the project

For this project you need to create and complete the two files: array_list.c and linked_list.c. In both files you need to write the code for each of the following functions (as declared in both the .h files):

  • char *list_at(struct List *list, int position)
  • struct List *list_construct()
  • void list_destruct(struct List *list)
  • int list_get_size(struct List *list)
  • int list_is_empty(struct List *list)
  • void list_output(struct List *list)
  • int list_push_back(struct List *list, char *item)
  • char *list_remove_at(struct List *list, int position)

Getting Started

The very first thing you should do is finish reading this document. There is useful information that you’ll want to be aware of so you can refer back to it when you reach the appropriate point.

The second thing you should do is read all the comments in list.h so it is clear what each function should do. Always make sure you understand what it is that you are being asked to do before attempting to do it.

Once you understand what you are being asked to do, literally draw out some of the operations. What should the structure look like after it’s allocated? What does the structure look like after a number of insert operations? What about after a number of remove operations? What are the error cases that you need to handle in each function?

Only after you’ve got an idea in your head about how the functions should create/manipulate/destroy the structure(s) should you start coding.

To start coding, you first need to define all the functions that are declared in list.h in their respective .c files: array_list.c for the array-based implementation, and linked_list.c for the link-based implementation. A proper definition requires a minimal implementation, so functions that have a non-void return type must return something of that type, and functions that are void must at least have an empty body, {}. In general when defining a minimal version of a function that returns a value, you should return a value that indicates failure.

Once all of the functions are defined for array_list.c you should be able to compile the program via make array without receiving any errors and warnings.

When you can compile without errors and warnings, implement each function one at a time and test each individually to convince yourself that the function works as expected. Use the provided test_list.c and main.c programs to help you test your functions. You can implement the functions in any order you wish. However, I strongly encourage you to think about the dependencies between functions and implement the ones without dependencies first.

Sample Execution

You are provided with two programs to help you test your code. Here we’ll give a sample of how to compile and run both.


If you want to test your array list implementation using the test_list.c program, you will want to compile via:

$ make test_array

Assuming there are no errors (can’t proceed) and warnings (you should always fix your warnings) then you can run the test program a few ways:

./test_array 0 -1

The above will attempt to run all tests available, starting at test 0, and running through the remainder (a negative second argument means run the remainder). Assuming your program works correctly you should see output like:

Test 00: construct_destruct             Passed
Test 01: at_0_after_push_back_one       Passed
Test 02: at_minus1_after_construct      Passed
Test 03: at_minus1_after_push_back_one  Passed
Test 04: at_neg1_after_push_back_one    Passed
Test 05: at_plus1_after_construct       Passed
Test 06: at_plus1_after_push_back_one   Passed
Test 07: get_size_after_construct       Passed
Test 08: get_size_after_push_back_one   Passed
Test 09: is_empty_after_construct       Passed
Test 10: is_empty_after_push_back_one   Passed
Test 11: output_after_construct         Passed
Test 12: output_after_push_back_one     Passed
Test 13: push_back_remove_at_0          Passed
Test 14: push_back_remove_at_neg1       Passed
Test 15: remove_at_0_after_construct    Passed
Test 16: remove_at_neg1_after_construct Passed

It’s possible that your program segfaults (or results in some other crash) on one of the tests. In such a case the output might look like:

Test 00: construct_destruct             Passed
Test 01: at_0_after_push_back_one       Segmentation fault (core dumped)

First, this is a hint that something broken in your code as a result of the at_0_after_push_back_one test. You should look at what that test does in test_list.c and fix it. However, should you want to see the result of the other tests, you can run the test program like so:

$ ./test_array 2 -1
Test 02: at_minus1_after_construct      Passed
Test 03: at_minus1_after_push_back_one  Passed
Test 04: at_neg1_after_push_back_one    Segmentation fault (core dumped)

Note that we changed the 0 to a 2 to begin testing at test 2. In the output that follows you see that we result in another segfault on test 4, at_neg1_after_push_back_one. We can then start at test 5 if we so desired, and continue this process to see all the tests that result in segfaults.

The testing process is the same for the link-based implementation. However, rather than running make test_array in combination with ./test_array you will want to use make test_linked in combination with ./test_linked.


main.c defines a program that allows you to enter in strings from standard input (or a given file) and add them to the list. It then outputs the contents of various items in the list, and attempts to remove each. If you want to test your array-based implementation compile via make array (make linked for the link-based implementation). Execute via:


(replace ./array_list with ./linked_list if you compiled via make linked) You will be prompted to enter strings via standard input. Assuming you insert the same strings as I have entered (shown along with the output) a sample run might look like:

Enter a string to add to the list (or empty to stop): one apple
Enter a string to add to the list (or empty to stop): two bananas
Enter a string to add to the list (or empty to stop): three something elses
Enter a string to add to the list (or empty to stop): 
  0: one apple
  1: two bananas
  2: three something elses
 First+: one apple
 First-: one apple
Middle+: two bananas
Middle-: three something elses
  Last+: three something elses
  Last-: three something elses
     -1: (null)
     +1: (null)
remove -1: (null)
remove +1: (null)
Removed: two bananas
  0: one apple
  1: three something elses
Removed: one apple
  0: three something elses
Removed: three something elses

You can also give a file as the input to the program. Execute like so:

./array_list Makefile

Tips and recommendations

Negative position values

Both list_at and list_remove_at require you to handle negative position values. While you can attempt to add additional conditionals to handle the positional value as both negative in positive in both of these functions, it’s much simpler (trust me) to simply convert negative values into a positive value. Because this conversion code should be identical in both list_at and list_remove_at, it makes sense to move that functionality into its own function. You’ll have to duplicate that function in both of your *.c files, but you should only have to write it once.

Resizing the array

When creating the array-based implementation it should be apparent that you will need to start with some initial size array that will need to be dynamically expanded when the List needs to store more items than available in the array. First, it’s usually a good idea to work with initial sizes that are a power of two, so 2, 4, 8, 16, 32 are all good starting sizes. To dynamically resize the array you will want to look at the realloc function that’s part of the malloc family as it’ll save you from having to (1) call malloc and (2) copy all the existing elements.

You can choose any scheme you want for how much to increase the size of the array, but keep in mind a trade-off between time complexity (how much time it takes to copy items), and space complexity (how much wasted space you have). In general, the accepted approach is to double the size each time the limit is reached. There’s no need to reduce the size of the array as items are removed, but you’re free to do it if you want.

Submitting the project

Please review the submission instructions as needed. On the submission site you will find the command you need to use to submit the project. Note that you may resubmit this project as many times as necessary up until the deadline. If you are working with a partner, make sure to group up using the submission system.


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