In this assignment, you are going to implement basic functionalities of simple social network platform called Cengram. This social network platform has simple functionalities such as register, follow user, create post, remove account. Your job is to simulate those procedures with your skills on C programming. A sample input file will be given to you for this homework. Don’t worry, the code for reading input is given to you already, you will only focus on implementing linked list operations to get the desired output. You are going to have hands-on experience on different topics: memory allocation, structs, linked lists, strings (char pointers).

1 Specifications

Overall design is like the following. Read each of the specifications carefully:

1. There are two main linked lists in the global scope. userProfiles and allPosts. userProfiles is a linked list, in which there are nodes that contain pointers to User structure. allPosts is also a linked list, in which there are nodes that contain pointers to Post structure. You will modify these lists when:
   • A new user is registered. When a new user is created, it should be appended to the end of userProfiles linked list. If there are no users, userProfiles pointer should be newly created Node*. If there are users, next node after the last user node should be newly created Node*.
   • A new post is created. When a new post is created, it should be inserted to allPosts according to the postId. If there are no posts, allPosts pointer should be newly created Node*.
   • A user account is removed. When a user account is deleted, all posts of the user should be removed from allPosts and user node should be removed from userProfiles.
2. All users have followers. followers member of User structure is a linked list of user nodes. When a user follows another user, a new node containing User* information should be created and appended to the end of the followers linked list of the followed user. Keep in mind that you should NOT allocate new memory for follower User object in follow operation. You should find existing User* information from userProfiles and use it for new follower node to preserve consistency.
3. All users have posts. posts member of User structure is a linked list of post nodes. When a new post is created, a new node containing Post* information should be created and appended to the end of the posts linked list of the author user (notice the difference with inserting to allPosts). Keep in mind that you should NOT allocate new memory for new post in post operation. You should find existing Post* information from allPosts and use it for new post node to preserve consistency.
4. Death is inevitable. Some of the users may pass away and accounts get deleted. When a user account is deleted:
   • Deleted user’s posts should be removed from allPosts.
   • User node should be removed from userProfiles.
   • followers linked list of other users and posts linked list of deleted user should be empty (first empty the list and set NULL later).
   • All details about User* should be removed and cleaned completely.

While doing these deletions, you should also change totalUserCount, totalPostCount, usernumOfPosts, user-numOfFollowers accordingly.

2 Structures

NODE
void* data
Node* next

Node: It is a structure for holding reference to any kind of data. Consider it as a container. It can contain integer pointer, char pointer, User pointer, Post pointer etc.

When Node pointers are chained, it becomes a linked list. If data in nodes are User pointers, it becomes User list. If data in nodes are Post pointers, it becomes Post list.

Figure 1: Linked list structure, one linked list to rule them all

Figure 2: User and Date structures

Figure 3: Post structure and author as User*

3 Input File

4.1 Number of users:

Specifies the number of users that joined to Cengram.

4.2 Registering Users

Each user has userId, username, birthday information given in each line. Birthday information has day, month, year fields. For instance, below code means that user ”eminem” has userId ”3” and birthday ”17.10.1972”. Also ”tupac” has userId ”5” and birthday ”16.6.1971”. You need to use Date structure for storing birthdays and User structure for storing users. All of the structures are given to you in ”Cengram.h” file.

3 eminem 17 10 1972 5 tupac

16 6 1971

In addition to these, you need to register these users into the userProfiles list in the global scope. You can just append at the end of userProfiles list. Also, totalUserCount variable in the global scope should be incremented.

Node* userProfiles: This linked list is a list of nodes, each of which contains reference to a User object. This list is changed when a new User is registered. New nodes are appended to the end.

Figure 4: Management of userProfiles in the global scope

4.3 Number of follows:

Specifies the number of follow actions between users of Cengram.

4.4 Following users

Each following action has 2 parameters: following user id and followed user id. For instance, as you can see in the example below, user1 follows user4 and user5 follows user2.

1 4

• 2

When users follow someone, following user information should be appended to the followers list of followed user. You can just append at the end of followers list. Also, numOfFollowers member of the followed user should be incremented.

• Number of posts:

Specifies the number of created posts belong to the users of Cengram.

Node* followers: This linked list is similar to userProfiles. It is changed when another User follows current User. New nodes are appended to the end.

USER int userId = 1 char* username = “ice_cube” ……….

Figure 5: Management of followers member of User

• Creating Posts (25 pts):

Each post is defined with a line containing postId, ownerUserId, number of characters in post content. The next line contains the post content. The example input below states that user5 wrote a post with postId ”6” and this post contains ”107” characters.

• 5 107

It ain’t about black or white ’cause we human. I hope we see the light before it’s ruined, my ghetto gospel

When users make posts, post information should be appended to the posts list of author user. You can just append at the end of posts list. Also, numOfPosts member of the author should be incremented.

Furthermore, you need to add new post information to the allPosts list in the global scope. For this list, you need to preserve post order by their postIds. At the end of the program execution, allPosts should be in ordered by postIds, in ascending order. Finally, don’t forget to increment totalPostCount in the global scope.

Node* posts: This linked list is a list of nodes, each of which contains reference to a Post object.

This list is changed when a new Post is added. New nodes are appended to the end.

Figure 6: Management of posts member inside User structure

Node* allPosts: This linked list is a list of nodes, each of which contains reference to a Post object. This list is changed when a new Post is registered. New nodes are inserted with respect to their postIds, to preserve ascending order.

Figure 7: Management of allPosts in the global scope

4.7 Number of removed users:

Specifies the number of users who later on decided to delete their accounts from Cengram.

4.8 Remove User Account

Each integer in the line is a deleted user id. Remove users COMPLETELY from the system. Below lines say that 2 user accounts are removed, one of them is user5 and the other one is user4.

2

5 4

Before you remove the user, you need to remove all references to the user, remove its posts, remove references to deleted posts, remove birthday information, remove username information etc. By completely means that you will leave no clue behind when you delete the user.

4 Clarifications, Hints & Tips

1. Start early!
2. Linked list in this homework can be used for storing list of any data structure. It can be confusing at first. However, nobody creates different structure for similar operations on different things. In real life, code repetition is avoided.
3. Go step by step. You can implement appending node to the end, and change it to appending node according to member comparison, you can implement finding a node with respect to a given property etc.
4. To preserve consistency about the data, you have to work on same User and Post pointers for userProfiles, user’s followers, allPosts, user’s
5. You can write your helper functions in Cengram.c file. However, you can not add new files or you can not change any of the structures given in Cengram.h.
6. You should create a new Node for adding follower to user=> You should find existing User* from userProfiles and use that pointer to fill data member of the newly created Node*. Don’t allocate a memory for User* again, only allocate memory for new Node*.
7. You should create a new Node for adding new Post’s to user=> You should find existing Post* from allPosts and use that pointer to fill data member of the newly created Node*. Don’t allocate a memory for Post* again, only allocate memory for new Node*.
8. Since Node structure has a member data which is a void pointer, you need to do type casting to read its values as User or Post.