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HW: Hello, CPPeers!
Overview
Objectives
1. Practice with classes (constructors, getters, setters, and encapsulation).
2. Working with dynamic memory and pointers.
3. Using vectors.
4. Additional practice with file I/O.
5. Additional practice with exceptions.
Introduction
Many of you love Piazza given the immediate help you can get by using the platform. Alas, Piazza will no longer
be available next semester and you are tasked with creating a replacement. You decide to use the skills you
have gained through this course to come up with the platform CPPeers! As you are a big fan of social media,
you decide to design this platform as a network of users and posts. You choose an object-oriented approach.
Getting Started
● Get the starter code
○ Network.h/.cpp: the class definition for the fabulous cppeers network; an interface to all
users, posts, and hashtags.
○ User.h/.cpp: the class definition for the users of the cppeers network.
○ Post.h/.cpp: the class definition for the posts on the network.
○ Tag.h/.cpp: the class definition for the hashtags included within posts.
○ main.cpp: this file is useful for testing your code locally; also, contains the choice menu.
● Get the data files
● Review the code.
○ Read header and source files.
○ Compile and run the initial state of the starter code and submit to Gradescope to get an idea of
the test cases.
○ Review the organization of the classes. The following UML class diagram shows relationships
among Network, User, Tag, and Post classes used for this program.
● Look at the dependencies in classes. Best to implement in approximately the following order:
1) Tag
2) Post
3) User
4) Network
5) main()
● Allowed includes:
○ <iostream>
○ <fstream>
○ <sstream>
○ <vector>
○ <string>
○ <cctype>
○ <stdexcept>
○ “Post.h”
○ “User.h”
○ “Tag.h”
○ “Network.h”
● Refer to the appendix as needed.
Recommendations
● As you develop your code, you only need to implement the methods/functions you need at the moment.
You don’t have to get everything done at once. It is not a good strategy to do so.
● You can utilize main.cpp to test the functions that you have implemented so far. Alternatively, you can
create a separate tester file with its own main function.
● Plan and think before you code (write test cases first).
● Test locally and start early.
Sample Execution
Welcome to CPPeers
The options are:
1. load data file and add information
2. show posts by user
3. show posts with hashtags
4. show most popular hashtag
9. quit
——–> Enter your option: 1
Enter filename: TAMU-csce121-small.txt
Added User ajitjain
Added User michaelm
Added Post 42412212 by ajitjain
Added Post 58687888 by michaelm
Added Post 42353253 by michaelm
Welcome to CPPeers
The options are:
1. load data file and add information
2. show posts by user
3. show posts with hashtag
4. show most popular hashtag
9. quit
——–> Enter your option: 2
Enter username: michaelm
When an #array is passed to a #function, it decays to a pointer.
You can use pass-by-reference, if you need multiple updated
values in the calling #function. It also helps save memory and
CPU cycles.
Welcome to CPPeers
The options are:
1. load data file and add information
2. show posts by user
3. show posts with hashtag
4. show most popular hashtag
9. quit
——–> Enter your option: 3
Enter tagname: #dynamic
When deallocating #dynamic arrays, use delete[].
Welcome to CPPeers
The options are:
1. load data file and add information
2. show posts by user
3. show posts with hashtags
4. show most popular hashtag
9. quit
——–> Enter your option: 4
#function
Requirements
● You will be implementing the four classes as well as the functions in main.cpp.
● Constructors should use member initialization lists.
● Exceptions should have meaningful descriptions.
● The program must compile without warnings or errors.
Post Class
We provide
● Post class definition (Post.h)
● Constructor (Post.cpp)
○ Post::Post(unsigned int postId, string userName, string postText)
■ Throw std::invalid_argument if any of the following are true:
● postId is zero
● userName is empty
● postText is empty
● Getters (Post.cpp)
○ unsigned int Post::getPostId()
○ string Post::getPostUser()
○ string Post::getPostText()
You implement in Post.cpp
● Methods / Member functions
○ vector<string> Post::findTags()
■ Return a vector containing unique candidate tags extracted from postText
● Tags are words within postText that begin with a ‘#’.
● Tags are not case-sensitive, i.e. #happy and #HAPPY are the same tag
● Remove punctuations (‘!’, ‘,’, ‘.’, ‘?’) at the end of each extracted
tag, if any.
● As an example, the following need to be treated as the same, and need to be
added as the lowercase version (#happy) to the vector:
○ #happy
○ #Happy
○ #HaPpY
○ #HAPPY
○ #happy!
○ #happy!!
○ and so on…
■ When finding tags, this function returns all candidate strings beginning with ‘#’.
● Note: The function does NOT filter out invalid Tags, such as #, #1a23, or #!
happy. Such checks are performed in Tag’s constructor (see Tag). Relatedly, the
reason for removing punctuation above is to identify unique candidate strings,
not validation.
User Class
We provide
● User class definition (User.h)
You implement in User.cpp
● Constructor
○ User::User(string userName)
■ Throw std::invalid_argument if any of the following are true:
● userName is empty
● userName does not start with a letter ‘a’ – ‘z’
● userName contains uppercase letters ‘A’ – ‘Z’
○ In other words it should be all lowercase letters
● Getters
○ string User::getUserName()
○ vector<Post*>& User::getUserPosts()
● Methods / Member Functions
○ User::addUserPost(Post* post)
■ If post is nullptr, throw std::invalid_argument
Tag Class
We provide
● class definition (Tag.h)
You implement in Tag.cpp
● Constructor
○ Tag::Tag(string tagName)
■ Throw std::invalid_argument if any of the following are true:
● tagName length is less than 2
● the first character of tagName is not ‘#’
● the second character in tagName is not from ‘a’ – ‘z’
● tagName contains uppercase letters ‘A’ – ‘Z’
○ In other words it should be all lowercase letters
● there is one or more consecutive punctuations at the end of the tagName (e.g.,
#happy!, #happy!?, etc.), where punctuation is one of the following: (‘!’,
‘,’, ‘.’, ‘?’)
● Getters
○ string Tag::getTagName()
○ vector<Post*>& Tag::getTagPosts()
● Methods / Member Functionsusername
○ Tag::addTagPost(Post* post)
■ If post is nullptr, throw std::invalid_argument
Network Class
We provide
● Network class definition (Network.h)
You implement in Network.cpp
● Methods / Member Functions
○ Network::addUser(string userName)
■ If a user with this name already exists, throw std::invalid_argument
● User names are not case sensitive. For example, the following are treated as the
same and added as the lowercase version (ajitjain)
○ ajitjain
○ AjitJain
○ AJITJAIN
○ AjItJaIn
○ and so on…
● Let any exceptions from the User constructor go through, i.e., do not catch
exceptions from the User constructor
● When creating a new User object, remember that we are working with dynamic
memory (Use the ‘new’ keyword to allocate memory on the heap)
● If no exception, add the user to the Network data member users, and at the end
of the function, output “Added User ” followed by the username to standard
output
○ Network::addPost(unsigned int postId, string userName, string
postText)
■ If a post with this id already exists or if no user with this name exists, throw
std::invalid_argument
■ Adding a post to the network is a multi-step process and includes message passing
among various components to accomplish the following:
● Creation of the post (see Post; remember we are working with dynamic memory)
● Addition of the post to the Network data member posts
● Addition of the post information to the corresponding user (see User)
● Extraction of candidate hashtags contained within the post (see Post)
● For each candidate hashtag: search (within the collection of tags stored in the
Network) OR create (see Tag; only if the tag does not exist and remember we
are working with dynamic memory)
○ Note: When attempting to create a Tag, if an exception is thrown (by Tag
constructor), catch the exception and resume processing for the next
candidate hashtag
○ Remember to add a newly created tag to the Network data member tags
● addition of the post information to each tag (see Tag)
■ Let any exceptions from the Post constructor go through, i.e., do not catch exceptions
from the Post constructor
■ If no exception, at the end of the function, output “Added Post ” followed by the post
ID, “ by ”, and username to standard output
○ Network::loadFromFile(string fileName)
■ If file could not be opened, throw std::invalid_argument
■ Refer to the Data Files section, which specifies the format of User and Post information
included in the file. Add users and posts as you read the lines from the file by calling
addUser() and addPost().
■ If the file content does not match the specified format, throw std::runtime_error.
This includes:
● User or Post entry not following the specified format
● Unknown entry (neither User nor Post)
■ Note: You throw std::invalid_argument only when the file could not be opened. If
there are std::invalid_argument thrown by add user and post operations, you catch
them here and throw std::runtime_error instead.
○ vector<Post*> Network::getPostsByUser(string userName)
■ If userName is empty or not found, throw std::invalid_argument
■ Note: Assuming you followed the multi-step process for addPost() above, you now do
not need to traverse all the posts in the Network
○ vector<Post*> Network::getPostsWithTag(string tagName)
■ If tagName is empty or not found, throw std::invalid_argument
■ Note: Assuming you followed the multi-step process for addPost() above, you now do
not need to traverse all the posts in the Network
○ vector<string> Network::getMostPopularHashtag()
■ Return the tag which occurs in the maximum number of posts. In case of a tie, return all
such hashtags. If the network has no hashtag, return an empty vector.
■ Note: A hashtag should be counted only once per post. Assuming you followed the multistep process for addPost() above, you now do not need to traverse all the posts in the
Network and extract tags again from each post.
main.cpp
Use the menu example in the Overview above to fill in the gaps when implementing the following helper
functions. You will need to uncomment the loop in main when you have finished all other tasks.
● void processPostsByUser(Network& cppeers)
● void processPostsWithHashtags(Network& cppeers)
● void processMostPopularHashtag(Network& cppeers)
Appendix
Data File Format
The information format is given below. Each line starts with the string User or Post, which identifies the type of
information. Based on the type of information, one or more values follow. In the case of User, the value that
follows is a username. In the case of Post, values that follow are PostId, UserName, and PostText.
Implementing the functions listed in the previous section will allow you to check whether the read information
is valid or not.
User Information Format
User UserName
Example
User ajitjain
Post Information Format
Post PostId UserName PostText
Example
Post 42412212 ajitjain When deallocating dynamic arrays, use delete[].
Example valid file
User ajitjain
User michaelm
Post 42412212 ajitjain When deallocating #dynamic arrays, use delete[].
Post 58687888 michaelm When an #array is passed to a #function, it
decays to a pointer.
Post 42353253 michaelm You can use pass-by-reference, if you need
multiple updated values in the calling #function. It also helps save
memory and CPU cycles.
Useful functions and classes
You may use any of the functionality provided by C++ strings and C++ vectors in your solution. Most students
may find the following operations useful:
● getline
○ An example of how to use this is provided in Cppeers-main.cpp
● vector
○ push_back(elem): Adds a new element elem at the end of the vector
○ size(): Returns the number of elements in the vector
○ More information about vectors is available in the Vector class Overview section
● istringstream
○ You already used this in a labwork. If you need to refresh your memory, an example of how to
use this is provided in Cppeers-main.cpp
Vector class Overview
std::vector is a C++ standard class that provides the functionality of dynamically allocated arrays. You can
learn more about C++ vectors in the documentation (link to std::vector documentation) or in the Zybook
readings.
A simple example of using std::vector to store a list of consecutive int values is below:
#include <iostream>
#include <vector>
int main() {
// n is not fixed (providing the same capability as dynamic arrays)
size_t n = 0;
std::cout << “Enter value of n: “;
std::cin >> n;
std::vector<int> v;
for (size_t i = 0; i < n; i++) {
v.push_back(i); // add i to the last position in v
}
// let’s print the elements in a vector
// we can use a for loop as before
for (size_t i = 0; i < n; i++) {
std::cout << v.at(i) << ” ” ;
}
std::cout << std::endl;
return 0;
}

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