Objectives

• Be able to use topics learned this semester (control structures, array, fileIO)
• Understand classes and create objects
• Develop a menu driven program

Background

If youve ever bought a book online, the booksellers website probably told you what other books you might like. This is handy for customers, but also very important for business.

In 2009, online movie-rental company Netflix awarded one million dollars to the winners of the Netfli x Prize. The competition simply asked for an algorithm that would

perform 10% better than their own algorithm. Making good predictions about peoples preferences was that important to this company. It is also a very happening field of research that lies at an intersection between math, machine learning and computer science.

So how might we write a program to make recommendations for books?

Consider a user named Rabia. How is it that the program should predict books Rabia might like? The simplest approach would be to make almost the same prediction for every customer. In this case, the program would simply calculate the average rating for all the books in the database, sort the books by rating and then from that sorted list, suggest the top 5 books that Rabia hasnt already rated. With this simple approach, the only information unique to Rabia used by the prediction algorithm was whether or not Rabia has read a specific book.

We could make a better prediction about what Rabia might like by considering her actual ratings in the past and how these ratings compare to the ratings given by other customers. Consider how you decide on movie recommendations from friends. If a friend tells you about a few movies that (s)he enjoyed and you also enjoyed them, then when your friend recommends another movie that you have never seen, you probably are willing to go see it. On the other hand, if you and a different friend always tend to disagree about movies, you are not likely to go to a movie this friend recommends.

A program can calculate how similar two users are by treating each of their ratings as an array/vector and calculating a similarity value based on some calculation (like a dot product, or a sum of squared differences) using the two arrays.

Once you have calculated the pairwise similarity between Rabia and every other customer, you can then identify whose ratings are most similar to Rabias. If another user, Suelyn, is most similar to Rabia, we would recommend to Rabia the top books from Suelyns list that Rabia hasnt already rated.

Project Goal and Design

In project 2, you will be creating a book recommender system. You will be creating a Library class that comprises objects from Book and User classes.

Specifications

• Create a new class Book, where each instance represents a book and the Library class stores an array of these books. Define the class in a header file and implement it in a separate cpp file.
• Create a new class User, where each instance represents a person and the ratings they have given to books.The Library class stores an array of these Define the class in a header file and implement it in a separate cpp file.
• Create a new class Library . Define the class in a header file and implement it in a separate cpp file.
• You will have to create an instance of Library class in main() and call the respective functions to perform various tasks.

Tasks: Lets do this!

Task 1: Book class

Create a Book class, with a separate interface file (Book.h) and an implementation file (Book.cpp), comprised of the following attributes:

The Book class has the following attributes:

Data members (private):
title: string	The title of the book
author: string	The author of the book
Member functions (public):
Default constructor	Set title and author to an empty string
Parameterized constructor	Takes two strings assigning title and author, in this order
getTitle()	Returns the title as a string
getAuthor()	Returns the author as a string
setTitle(string)	Sets the players name (and returns nothing)
setAuthor(double)	Sets the players points (and returns nothing)

Sample test cases (Be sure to test all methods!)	Expected outputs
Book hungerGame(The Hunger Games,Suzanne Collins); cout << hungerGame.getTitle() << endl; cout << hungerGame.getAuthor() << endl;	The Hunger GamesSuzanne Collins

For the zip submissions, the files should be named as Book.h and Book.cpp. Your implementation should be organized nicely into separate files. For the code runner, paste your Book class and its implementation (both Book.h and Book.cpp) in the answer box. Please make sure to test your Book class on your Cloud 9 / VS code before submitting it to the code runner.

Task 2: User class

Create a User class, with a separate interface file (User.h) and an implementation file (User.cpp), comprised of the following attributes:

The User class has the following attributes:

Data members (private):
username: string	The name of the user
ratings: an array of integer	An array of integers (size 50) where all the ratings are stored
Member functions (public):
Default constructor	Set username to an empty string, and initialize all elements of the ratings array to 0
setUsername(string)	Takes a string to set username (and returns nothing)
setRatingAt(int, int)	Takes an index i and a rating value. If the index and the rating value are valid, assign the rating at the index.
getUsername()	Returns the name of this user ( string)
getRatingAt(int)	If i is within the bounds of the ratings array, it returns the rating value at index i of the ratings array. If not, it returns -1.

User class method: setRatingAt(int, int)

This setter takes the index of the rating to be set, and the rating value to set it to. If the index is within the bounds of the ratings array and the rating value is between 0 and 5, the function sets the rating value at the index and returns true. Otherwise, it returns false.

Rating	Meaning
0	Did not read
1	Hell no hate it!!
2	Dont like it.
3	Meh neither hot nor cold
4	Liked it!
5	Mind blown Loved it!

Method specifications:

• The method name: setRatingAt
• The method takes parameters in this order:
  • An index of the book, int

A new rating value, int

• The method sets the new rating value if the index is within the bounds of the rating array and the rating value is valid (i.e. between 0 and 5).
• The method returns a boolean value depending on the following cases:
  • True if it successfully updated the rating

False if it did not

User Class Method: getRatingAt(int)

This getter takes the index of a rating. If the index is within the bounds of the ratings array, then it returns the rating value at the index. If not, it returns -1.

Method specifications:

• The method name: getRatingAt
• The method takes parameters in this order:
  • An index of the book, int
• The method returns an integer value:
  • It returns the rating value if the index is within the boundary of the rating array

It returns -1 if the index is outside of the bounds of the ratings array

Sample test cases (Be sure to test all methods!)	Expected outputs
User hector; hector.setUsername(Hector Ramirez); hector.setRatingAt(0,4); cout << hector.getUsername() << endl; cout << hector.getRatingAt(0) << endl;	Hector Ramirez4

For the zip submissions, the files should be named as User.h and User.cpp . For the code runner, paste your Book class and its implementation (both User.h and User.cpp ) in the answer box. Please make sure to test your User class on your Cloud 9 / VS code before submitting it to the code runner.

Task 3: Library Class

Create a Library class, with a separate interface file (Library.h) and an implementation file (Library.cpp), comprised of the following attributes:

The Library class has the following attributes:

Data members (private):
books: an array of Book objects	The books in the library. Its size is 50 (constant)
users: an array of User objects	The users in the library. Its size is 100 (constant)
numBooks: int	The number of books in the library
numUsers: int	The number of users in the library
Member functions (public):
Default constructor	Sets both numBooks and numUsers to 0
getNumBooks()	Returns numBooks as an integer
getNumUsers()	Returns numUsers as an integer
readBooks(string)	Takes a file name (a string), reads a list of books, and stores them into the books array for this library. It returns the total number of books stored in the books array as an integer.
readRatings(string)	Takes a file name (a string), reads a list of users and their ratings and stores them into the users array for this library. It returns the total number of users stored in the users array as an integer.
viewRatings(string, int)	Takes a username and a minimum rating value. It prints all the books that the user has rated with a value greater than or equal to the minimum rating value. The function does not return anything.
printAllBooks()	Prints all books stored in the books array with average ratings. The function does not return anything.
addUser(string)	Takes a username and adds a user with that name to the users array. The function does not return anything.
updateRating(string,string	Takes username, title, and a new rating (in this order )
,int)	and updates the rating value of this title for this user. The function does not return anything.
getRecommendations(string)	Takes the username and prints the first 5 book recommendations. The function does not return anything.

Library Class Method: readBooks(string)

It takes a file name, reads a list of books, and stores them into the books array. Each line has an author and a title separated by a comma. The function returns the number of the total books stored in the books array. If the file cannot be opened, the function should return -1 .

Sample file (books.tx t) :

Douglas Adams,The Hitchhikers Guide To The Galaxy

Richard Adams,Watership Down

Mitch Albom,The Five People You Meet in Heaven

Laurie Halse Anderson,Speak

Maya Angelou,I Know Why the Caged Bird Sings

Jay Asher,Thirteen Reasons Why

Method specifications:

• The method name: readBooks The method parameter:
  • A filename, string
• The function returns an integer value depending on the following conditions (checked in this order)
  • It returns -1 if the file cannot be opened.

It returns the total number of books if the books array is full

It returns the total number of books stored in the array if it can successfully read the list of books.

• Important:
  • The method stores all the books stored without replacing them. For example, if it reads a file with 5 books (the first time it is called) and then another file with 3 books (the second time it is called), then all 8 books should be stored in the books array and it returns 8 (the second time it is called).

How to test it?

• You can test the method is working or not by 1) calling it in your main and see if it returns the correct value, 2) calling it multiple times to see if the function returns the total number of the books stored in the array, 3) implement the other methods (viewRatings and printAllBooks) to see if it prints the books stored in the array

Library Class Method: readRatings(string)

It takes a file name and reads usernames and their ratings. A username is stored on one line, and the users ratings are stored on the following line, separated by commas.

Sample file (ratings.tx t):

cynthia

4,3,1,0,3,0,5,1,5,2,2,2,1,4,4,2,0,1,1,2 diane

3,1,1,0,2,2,3,1,0,1,4,3,1,2,1,1,5,2,4,0 joan

3,1,2,0,2,2,4,3,0,2,2,4,5,2,2,1,4,1,1,3

In the above sample file, Cynthia rated 4 for the book at index 0 , rated 3 for the book at index 1, and so on. Diane rated 3 for the book at index 0, rated 1 for the book at index 1.

Each rating is mapped to the book by the index. As shown in below, the rating value at index 0 of the ratings array (for any particular user) will be that users rating for the book at index 0 of the books array. The same holds for ratings and books at all other indices of the ratings and books arrays.

Method specifications:

• The method name: readRatings The method parameter:
  • A filename, string
• The function returns an integer value depending on the following conditions (in this order)
  • It returns -1 if the file cannot be opened.

It returns the total number of users if the users array is full

It returns the total number of users stored in the array if it can successfully read the list of users and ratings.

• Important:
  • The method stores all the users stored without replacing them. For example, if it reads a file with 5 users (the first time it is called) and then another file with 3 users (the second time it is called), then all 8 users and their ratings should be stored in the users array and it returns 8 (the second time it is called).

How to test it?

You can test the method is working or not by 1) calling it in your main and see if it returns the correct value, 2) calling it multiple times to see if the function returns the total number of the users stored in the array, 3) implement the other methods (viewRatings and printAllBooks) to see if it prints the users and their ratings stored in the array

Library Class Method: viewRatings(string, int)

It takes a username and a minimum rating value. It prints all the books the user has rated with a value that is greater than or equal to the minimum rating value in the format as shown below. The username search should be case insensitive (i.e. Ben , BEN , BeN are the same ben ) . Recall that a rating value of 0 means that the user has not rated the book yet.

Expected output format:

Here are the books that megan rated

Title : The Hitchhikers Guide To The Galaxy

Rating : 5

Title : The Five People You Meet in Heaven

Rating : 2

Method specifications:

• The method name: viewRatings
• The method parameters (in this order):

A username, string

A minimum rating, int

• The function does not return anything.

Edge cases (should be handled in this order):

• The library has not been initialized yet. If there are no books or no users in the array, it cannot print the ratings. Display the following message:

The library has not been fully initialized.

• There might be a case where the user does not exist. When you search for a username, it should be case insensitive. If the username is not found, then it displays the following message. < username> is an actual username passed into the method.

<username> does not exist.

• If you find a username, but there are no ratings that are greater than or equal to the minimum rating value, display the following message:

<username> has not rated any books with <min rating> or higher.

Sample Run 1 for Akriti with minRating = 4 ( books_mini.tx t and users_mini.tx t) :

Here are the books that Akriti rated

Title : Title1

Rating : 5

Title : Title5

Rating : 4

Sample Run 2 for Keya with minRating = 2 ( books_mini.tx t and users_mini.tx t) :

Keya has not rated any books with 2 or higher.

How to test it?

After creating an instance of the Library class, you can call readBooks and readRatings methods, then call viewRatings to see if you can get the same output as above.

Library Class Method: printAllBooks()

It would be helpful to see a list of all the books stored in the array, along with their average ratings. The average rating should be formatted with two-digit precision. If the rating value is 0, it means that the user has not rated the title yet. So we dont include it in the calculation.

Methods specifications:

• The method name: printAllBooks
• The method does not take any parameters.
• The function does not return anything.

Edge case:

• The library has not been initialized yet. If there are no books or no users in the array, it cannot print the ratings. Display the following message:

The library has not been fully initialized.

Sample Run: (books_mini.tx t and users_mini.tx t):

(3.33) Title1 by Author1

(3.00) Title2 by Author2

(2.67) Title3 by Author3

(4.00) Title4 by Author4

(3.00) Title5 by Author5

How to test it?

After creating an instance of the Library class, you can call readBooks and readRatings methods, then call printAllBooks to see if you can get the same output as above.

Library Class Method: updateRating(string,string,int)

It takes a username, title of a book, and the users new rating for the book. It updates the rating value if the username and title exist in the arrays and the rating value is valid (between 0 and 5). When you search for a username and title, it should be case insensitive (i.e. Ben , BEN , BeN are the same ben ).

Methods specifications:

• The method name: updateRating
• The method parameters (in this order):

A username, string

A title, string

A new rating, int

• The function does not return anything.

cases: (should be handled in this order):

• The library has not been initialized yet. If there are no books or no users in the array, it cannot print the ratings. Display the following message:

The library has not been fully initialized.

• There might be a case where the user does not exist. When you search for a username, it should be case insensitive. If the username is not found, then it displays the following message. < username> is an actual username passed to the method.

<username> does not exist.

• If the new rating value is invalid, we cannot update the rating value. Valid ratings are between 0 and 5 (inclusive). If the new rating value is invalid, then display the following message:

<rating> is not valid.

• There is also a case where the title does not exist in the library. If so, display the following message: < title> is an actual book title passed to the method.

<title> does not exist.

• Once we check all the above conditions, we can update the users rating for the given title. If it is successful, then display the following message:

The rating has been updated.

Library Class Method: addUser(string)

We always get new users. Lets create a method to add a new user to the library. It takes a username and adds it to the users array, provided the username does not already exist and there is a space in the array. When you search for a username, it should be case insensitive

(i.e. Ben , BEN , BeN are the same ben ).

Methods specifications:

• The method name: addUser The method parameter:

A username, string

• The function does not return anything.
• The new user has not rated any books yet. So all the ratings for the new user should be

cases: (should be handled in this order):

• The library might not have a space to add a new user. (It already has 100 users). If so, display the following message. < username> is an actual username passed into the

The library is already full. <username> was not added.

• There might be a case where the user already exists. When you search, it should be case insensitive (i.e. Ben, ben, BEN are the same ben). If the username already exists in the users array, print the following message:

<username> does already exist.

• Once you check that there is a space in the users array and the username does not exist, then the username should be added. If successful, print the following message:

Welcome to the library <username>

Library Class Method: getRecommendations(string)

It will recommend book titles a user might enjoy based on the ratings of another user who likes similar books.

Methods specifications:

• The method name: getRecommendations The method parameter:

A username, string

• The function does not return anything.

How to find books to recommend?

You recommend books based on the most similar user. You can calculate how similar two users are by calculating the sum of square differences (SSD).

The SSD is calculated by summing the squares of the differences between the corresponding elements in the two ratings array of two users. Because our similarity metric is based on difference, more similar users will have smaller similarity values. Lets say we want to generate recommendations for Ben. In the equation below, A represents Bens rating for i th book and B represents the other users rating for i th book.

Once you find the user most similar to the given user (Ben in this example), print the first 5 books that the most similar user rated as 3 or higher, that the given user (Ben) has not rated yet (i.e. the rating is 0).

Note: If the user has not rated any books, then the user cannot be the most similar user.

For example, suppose we have 5 books (stored in the books array in this order):

Lab Girl

The Rosie Project

The Catcher in the Rye

Unbelievable

A Man of the People

And 5 users in the users array in the library:

Akriti:	[5, 0, 2, 0, 4]
Malvika:	[4, 3, 3, 5, 4]
Vipra:	[0, 0, 0, 0, 1]
Monika:	[0, 0, 0, 0, 0]
Keya:	[1, 0, 3, 3, 0]

Based on the above data, If you find recommendations for Akriti, then calculate the similarity between:

Once you calculate the pairwise SSD between Akriti and every other user, you can then identify the user whose ratings are most similar to Akritis. In this case, 17 is the smallest SSD value among the users. Therefore, Malvika is the most similar to Akriti.

Once you figure out the most similar user, print the first 5 books the most similar user (Malvika) rated 3 or higher, that the given user (Akriti) has not rated yet. In this case, it prints the following books:

The Rosie Project

Unbelievable

Akriti has not rated Book1 and Book3 and Malvika rated those books 3 o r higher, so it prints them.

Based on the above data, If you find recommendations for Vipra, then we do the same calculation for the SSD score:

• Vipra and Akriti: SSD = 38
• Vipra and Malvika: SSD = 68
• Vipra and Monika: SSD = 1
• Vipra and Keya: SSD = 20

In this case, the most similar user should be Keya. The SSD between Vipra and Monika are the lowest (SSD = 1). However, since Monika has not rated any books yet (all the ratings are 0), she cannot be the most similar user.

Once you figure out the most similar user, you find the books in which Vipra has not rated and Keya rated 3 or higher. Then, it will prints:

The Catcher in the Rye

Unbelievable

Vipra has not rated the first four books, but of these, the books Keya liked (rating is 3 or higher) are only The Catcher in the Rye and Unbelievable.

Edge cases (in this order):

• The library has not been initialized yet. If there are no books or no users in the library, it cannot find recommendations. Display the following message:

The library has not been fully initialized.

• There might be a case where the user does not exist. When you search, it should be case insensitive (i.e. Ben, ben, BEN are the same ben). If the username does not exist in the users array, print the following message:

<username> does not exist.

• After you find the most similar user, but there might be no books to recommend at the moment. If so, display the following message:

There are no recommendations for <username> at present.

• There might be the case where there are more than 5 books to recommend. In that case, we recommend only the first 5 books.

Sample Run: Recommendations for Akriti : (books_mini.tx t and users_mini.tx t):

Here is the list of recommendations

The Rosie Project by Graeme Simsion

Unbelievable by Katy Tur

Sample Run: Recommendations for Vipra : (books_mini.tx t and users_mini.tx t):

Here is the list of recommendations

The Catcher in the Rye by J. D. Salinger

Unbelievable by Katy Tur

Sample Run: Recommendations for Malvika : (books_mini.tx t and users_mini.tx t) :

There are no recommendations for Malvika at present.

The most similar user for Malvika is Akriti (SSD = 36). However, Malvika has rated all the books Akriti has rated, so there are no books to recommend.

For the zip submissions, the files should be named as Library.h and Library.cpp. For the code runner, paste your Book class and its implementation, User class, Library class and its implementation (both Book.h, Book.cpp, User.h, User.cpp, Library.h and Library.cpp) in the answer box. Please make sure to test your Library class on your Cloud 9 / VS code before submitting it to the code runner.

Task 4: Lets make main()

Now, lets put it all together in the main() function. Create a project.cpp and write the main() function in the file. To make it user-friendly, well create a menu option and call the appropriate methods (that you created) for each option.

The menu has the following options:

Select a numerical option:

======Main Menu=====

1. Read books
2. Read ratings
3. View ratings
4. Print all books
5. Update a rating
6. Add a user
7. Get recommendations
8. Quit

The menu will run in a loop, continually offering the user the options until they opt to quit. You need to fill in the code for each of the options. Be sure to use the methods you wrote in Task 3.

Invalid option: If the user enters invalid option, then print

Invalid option.

Option1: Read books

The program asks for a filename of a book list and displays the total number of the books stored in the array. If the file cannot be opened, then it prints No books saved to the database.

Sample Run 1 (bold is user input)

Enter a book file name:

books.txt

Total books in the database: 50

Sample Run 2 (bold is user input)

Enter a book file name:

this_file_does_not_exist.txt

No books saved to the database.

Option2: Read ratings

The program asks for a filename of a rating list and displays the total number of the users stored in the array. If the file cannot be opened, then it prints No users saved to the database.

Sample output 1 (bold is user input)

Enter a user file name:

ratings.txt

Total users in the database: 50

Sample Run 2 (bold is user input)

Enter a user file name:

this_file_does_not_exist.txt

No users saved to the database.

Option3: View ratings

The program asks for a username and a minimum rating value. Then, it calls the viewRating method.

Sample Run (bold is user input)

Enter a user name:

Akriti

Enter a minimum rating:

2

Here are the books that Akriti rated

Title : Lab Girl

Rating : 5

Title : The Catcher in the Rye

Rating : 2

Title : A Man of the People

Rating : 4

Option4: Print all books

If option 4 is selected, then it will call the printAllBooks method.

Option5: Update users rating

The program asks for a username, a title, and a new rating. Then, it will call the updateRating method.

Sample Run (bold is user input)

Enter a user name:Akriti Enter a book title: The Catcher in the Rye Enter a new rating:3 The rating has been updated.

Option6: Add a user

The program asks for a username. Then, it will call the addUser method.

Sample Run (bold is user input)

Enter a user name:

Divya

Welcome to the library Divya

Option7: Get recommendations

The program asks for a username. Then, it will call the getRecommendations method.

Sample Run 1 (bold is user input)

Enter a user name:

Akriti

Here is the list of recommendations

The Rosie Project by Graeme Simsion

Unbelievable by Katy Tur

Option8: Quit

Before exiting the program, print Good bye!

For the zip submissions, the files should be named as project.cpp. For the code runner, paste your main(), Book class and its implementation, User class, Library class and its implementation (both Book.h, Book.cpp, User.h, User.cpp, Library.h and

Library.cpp) in the answer box. Please make sure to test your main on your Cloud 9 / VS code before submitting it to the code runner.