Assignment 1: Word Lists

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Assignment 1: Word Lists

Your task is to create a class called `Wordlist` that stores words without any
duplicates. When it’s done, you’ll be able to add and remove words from it, and
also create an index of all its words in alphabetical order.

`Wordlist` *must* use a **doubly-linked list** as its underlying representation.
Vectors, arrays, or other container data structures are *not* allowed, except
for one case described below: the method `get_sorted_index()`, which returns a

## Getting Started

All the code you’ll submit for this assignment goes in [Wordlist.h](Wordlist.h).
*Don’t* put `main` in [Wordlist.h](Wordlist.h). Instead, put `main` in
[a1_main.cpp](a1_main.cpp). In `main` you should call the testing code for your
`Wordlist` class.

> **Note** You can download all the files for this assignment in a single .zip
> archive from the [Github repository for the course](
> Click on the green “Code” button, and then click on “Download ZIP”.

### Implement the Methods in Wordlist_base

Write your implementation of `Wordlist` in [Wordlist.h](Wordlist.h). It must
publicly inherit from `Wordlist_base`, and use the `Node` `struct` (given in
`Wordlist`) to implement a doubly-linked list.

[Wordlist.h](Wordlist.h) has the class `Wordlist` where you should implement all
the virtual methods listed in the `Wordlist_base` class (in

Most of the methods in `Wordlist_base` are *virtual* and *abstract*, and so you
*must* write your own version of them in `Wordlist`. `first_word()` and
`last_word()` have implementations that you *cannot* change.


– **Do not** change [Wordlist_base.h](Wordlist_base.h) in any way: keep it
exactly as-is.
– **Do not** use vectors, arrays, or any other data structures in
[Wordlist.h](Wordlist.h). The one and only exception is the method
`get_sorted_index()` that returns a `vector<string*>`.

### Implement Constructors, and a Destructor

In addition to the virtual methods listed in `Wordlist_base`, in your `Wordlist`
class write a *default constructor* that takes no parameters and creates an
empty `Wordlist` object:

// Pre-condition:
//     none
// Post-condition:
//     Creates an empty Wordlist object.
// Performance:
//     It should always take a very small, constant amount of time.

You would use it like this:

Wordlist lst;

// … lst is an empty Wordlist object …

Write a *copy constructor* that takes another `Wordlist` as input, and
initializes the new `Wordlist` to contain copies of all the strings in the other
`Wordlist`. The copied `Wordlist` should **not** be modified in any way:

// Pre-condition:
//     other is a valid Wordlist object
// Post-condition:
//     Creates a new Wordlist object that is a copy of other; other is not modified
//     in any way, and other and the new object do not share any values. If other
//     is frozen, then the new object is also frozen.
// Performance:
//     The running-time should be proportional to the number of words in other.
Wordlist(const Wordlist& other);

Write one more constructor that takes the name of a text file as input, and
initializes the list by adding all the words in the file to the list. For
simplicity, you can assume that the file is a text file that always exists:

// Pre-condition:
//     filename is the name of a text file that exists
// Post-condition:
//     Creates a new Wordlist object that contains all the words in the file
//     filename. If the file contains duplicate words, then the new Wordlist
//     object will contain only one copy of each word.
// Performance:
//     The number of calls to add_word should be proportional to the
//     length of other (or better).
// Note:
//     For this constructor a “word” is defined as the string return by the
//     >> operator. See the read_from_terminal() function for example of how
//     to use >> to read words.
Wordlist(const string& filename);

Write a destructor for `Wordlist` that de-allocates all the nodes in the list.
Make sure to test this by running your program with `valgrind` (described
below). Note that in `Wordlist_base` the destructor is called
`~Wordlist_base()`, while the one you write for `Wordlist` is called

### Frozen and Unfrozen Wordlists

A `Wordlist` is either **frozen** or **unfrozen**. Initially, a `Wordlist` is
*unfrozen*, and any method can be called on it.

When the `get_sorted_index()` method is called, the `Wordlist` automatically
becomes *frozen*. This means that it can no longer be modified: calling
`add_word()` or `remove_word()` on a frozen lists causes them to throw a
`runtime_error` exception. All other methods work the same as on an *unfrozen*

The reason for this feature is that by freezing the list after calling
`get_sorted_index()` we can guarantee that the pointers in the returned vector
are always valid as long as the list still exists.

> **Note** As you implement and test `Wordlist`, think about whether or not you
> believe this freezing feature is a good one. Maybe it is too inconvenient, or
> makes some code more complicated to write? But if you don’t use freezing, then
> how could you be sure that the pointers in the returned vector are always
> pointing to valid values?

### Testing Your Code

You can use the `read_from_terminal()` function in [a1_main.cpp](a1_main.cpp) to
help test your code. For example, [small.txt](small.txt) contains:

This is
a test
or is this
a test?


When you run:

// …

void read_from_terminal()
Wordlist lst;
string w;
while (cin >> w)

// print the words in sorted order
vector<string *> index = lst.get_sorted_index();
for (int i = 0; i < index.size(); i++)
cout << (i + 1) << “. ” << *index[i] << endl;

int main()

You should get this output:

❯ ./a1_main < small.txt
1. This
2. a
3. is
4. or
5. test
6. test?
7. this

Notice that *case matters*, e.g. `”This”` and `”this”` count as *different*
words. Also, punctuation *matters*, e.g. `”test”` and `”test?”` are different.

> **Note** Real life programs would likely strip out punctuation and perhaps
> ignore letter case. But in this assignment we want to count every word exactly
> as it appears in the file. This makes the code a littler simpler, and more
> consistent across students.

Here’s another example using the file [sonnet30.txt](sonnet30.txt):

❯ ./a1_main < sonnet30.txt
1. All
2. And
3. But
4. For
5. I
6. The
7. Then
8. When
9. Which
10. a
11. account
12. afresh
13. an
14. and
15. are
16. as
17. at
18. before.
19. can
20. cancell’d
21. dateless
22. dear
23. death’s
24. drown
25. end.
26. expense
27. eye,
28. flow,
29. fore-bemoaned
30. foregone,
31. friend,
32. friends
33. from
34. grievances
35. grieve
36. heavily
37. hid
38. if
39. in
40. lack
41. long
42. losses
43. love’s
44. many
45. moan
46. moan,
47. my
48. new
49. night,
50. not
51. of
52. old
53. on
54. o’er
55. paid
56. past,
57. pay
58. precious
59. remembrance
60. restor’d
61. sad
62. sessions
63. sigh
64. sight:
65. silent
66. since
67. sorrows
68. sought,
69. summon
70. sweet
71. tell
72. the
73. thee,
74. thing
75. things
76. think
77. thought
78. time’s
79. to
80. unused
81. up
82. vanish’d
83. wail
84. waste:
85. weep
86. while
87. with
88. woe
89. woe,
90. woes

Checking output manually is hard to do with long lists, so here is another handy

❯ ./a1_main < sonnet30.txt > sonnet30_sorted_output.txt

The expression `> sonnet30_sorted_output.txt` re-directs everything `a1_main`
writes to `cout` into the file
[sonnet30_sorted_output.txt](sonnet30_sorted_output.txt). You can view
[sonnet30_sorted_output.txt](sonnet30_sorted_output.txt) in a text editor, or by
running these commands:

❯ cat sonnet30_sorted_output.txt
… contents of sonnet30_sorted_output.txt …

❯ more sonnet30_sorted_output.txt
… contents of sonnet30_sorted_output.txt a page at a time …

Another useful command is `diff fileA fileB`, which finds differences between
text files `fileA` and `fileB`. You can use it to check the output of your
program. For example, if you run [sonnet30.txt](sonnet30.txt) through
`read_from_terminal()` and save the output to `my_sonnet30_sorted_output.txt`,
then you can check your output like this:

> diff my_sonnet30_sorted_output.txt sonnet30_sorted_output.txt


If the files have the same content, then nothing is printed. Otherwise, all
differences are printed.

Here’s one more example. The file [tiny_shakespeare.txt](tiny_shakespeare.txt)
has over 200,000 words:

❯ ./a1_main < tiny_shakespeare.txt > tiny_shakespeare_sorted_output.txt

The file
[tiny_shakespeare_sorted_output.txt](tiny_shakespeare_sorted_output.txt) lists
25,670 unique words in alphabetical order.

## What to Submit

When you’re done, submit just your [Wordlist.h](Wordlist.h) on Canvas, and
nothing else.

The marker will use their own `a1_main.cpp` that #includes your
[Wordlist.h](Wordlist.h) and will test the methods in it.

The marker will compile their code on Ubuntu Linux using [makefile](makefile)
like this:

> make a1_main
g++ -O3 -std=c++17 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g a1_main.cpp -o a1_main

A copy of [Wordlist_base.h](Wordlist_base.h) will be in the same folder as your
[Wordlist.h](Wordlist.h) when it’s compiled.

**Important** The compilation command is very strict: no warnings, errors, or
unused variables are allowed. Make sure to compile your code with this command
before submitting it.

## Grading

The marker will test the correctness of your code on data you have not seen
before, and they will also test individual method calls using test functions you
have not seen.

They will run your program with `valgrind` to check for memory leaks and other
memory errors, e.g.:

> valgrind ./a1_main < small.txt
==13731== Memcheck, a memory error detector
==13731== Copyright (C) 2002-2017, and GNU GPL’d, by Julian Seward et al.
==13731== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==13731== Command: ./a1_main
1. This
2. a
3. is
4. or
5. test
6. test?
7. this
==13731== HEAP SUMMARY:
==13731==     in use at exit: 0 bytes in 0 blocks
==13731==   total heap usage: 10 allocs, 10 frees, 78,160 bytes allocated
==13731== All heap blocks were freed — no leaks are possible
==13731== For lists of detected and suppressed errors, rerun with: -s
==13731== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Be sure to test your program thoroughly with `valgrind` before submitting it.

`valgrind` should report “no leaks are possible”, and should *not* print any
other errors. Note that it is possible for your program to have a memory leak
that does not occur on some runs of your program, so be sure to test your
program thoroughly.

> **Important** You need to follow these instructions exactly. If you submit a
> program that doesn’t compile, or that crashes, or that has memory leaks, then
> you will will lose marks. It is up to you to test your program to make sure it
> works correctly with these instructions.

## Marking Scheme

### Methods: 22 marks

– **2 marks** for each of the 8 virtual methods in `Wordlist_base` that are
implemented correctly. This includes the destructor.
– **2 marks** for the `Wordlist_base` *default constructor* described above.
– **2 marks** for the `Wordlist_base` *copy constructor* described above.
– **2 marks** for the `Wordlist_base` constructor described above that reads
words from a file.

### Overall source code readability: 5 marks

– All code is sensibly and consistently indented, and all lines are 100
characters in length, or less. **Hint**: In the Linux command-line you can
print all the lines in a file with more than 100 characters with this command
(the initial `>` is the prompt character, so don’t type it):

> awk ‘length > 100’ some_file.cpp

If this prints nothing, then the file has no lines over 100 characters long.

– Whitespace is used to group related pieces of a code to make it easier for
humans to read. All whitespace has a purpose.
– Variable and function names are self-descriptive.
– Appropriate features of C++ are used, as discussed in the course. **Note** If
you use a feature that we haven’t discussed in class, **you must explain it in
a comment**, even if you think it’s obvious.
– Comments are used when needed to explain code whose purpose is not obvious
from the code itself. There should be *no* commented-out code from previous
– Source code readability marks may be deducted for code that is unreadable in
some way not covered by the above. The deduction is proportional to how
serious the problem is.

### Deductions

– **-5 marks** if valgrind reports any memory leaks or other errors during the
markers test runs
– **-5 marks** if your program crashes on any valid test input
– **a score of 0** if you:
– change `Node` in a way, if you modify anything in `Wordlist_base`, or if you
use a `vector`, array, or any other data structure other than a list; the
one exception is for the method `get_sorted_index()` that returns a
– have no statement of originality, or it’s modified in any way.
– at least **-1 mark** if your file has an incorrect name, or you submit it in
an incorrect format, etc.; possibly multiple deductions if there are multiple
– at least **-1 mark** if you submit a non-working file
– if the marker can easily fix your file and make it work, then there is only a
small deduction
– if the marker has to spend a lot of time fixing your file, then there is a
larger deduction; if they can’t make it work, then they you will get 0

## Hints

Test as you go! Don’t wait until after you write all the code to test it. When
you write a method, add a few test cases for it, e.g. using `assert` or


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