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Linked List

Communication Between Towers

● Create, traverse, add, and delete nodes in a linked-list

Communication between towers

In the Lord of the Rings trilogy, there is a scene where the first beacon is lit in the towers of Minas Tirith. The second beacon then sees the fire, and knows to light its fire to send a signal to the third beacon, and so forth. This was a means of communicating in the days before telegraphs were invented as it was much faster than sending a human rider to deliver a message. Communication towers were equipped with signaling mechanisms, such as mirrors, that could spell out messages using the positions of the mirrors.

Today, there are several ples of communication networks that are conceptually similar, but much more technically advanced, that route messages through multiple hubs between the sender and the receiver. For ple, when you type a URL into a web browser, a request is sent through a network of service providers to the destination, and then packets of information are sent back to your machine.  If I type www.google.com from my home in Boulder, my request follows this path:

1 (

2 c-24-9-60-1.hsd1.co.comcast.net (

3 te-9-7-ur02.boulder.co.denver.comcast.net

4 xe-13-3-1-0-ar01.aurora.co.denver.comcast.net

5 he-3-10-0-0-cr01.denver.co.ibone.comcast.net (

te-1-1-0-4-cr01.chicago.il.ibone.comcast.net (

6 xe-2-0-0-0-pe01.910fifteenth.co.ibone.comcast.net (

7 as15169-1-c.910fifteenth.co.ibone.comcast.net (

8 (

9 (

10 den03s06-in-f16.1e100.net (

Each IP address is a hop in the network for my request, which is received at each service provider and then forwarded to the next service provider in the network, depending on the final destination of the message.

(Note: I got this path by typing traceroute www.google.com in a terminal window. From campus, you will see a different path.)

Build your own communications network
Overview: In this project, you’re going to simulate a communications network using a linked list. Each node in your linked list will represent a city and you need to be able to send a message between nodes from one side of the country to the other. Your program also needs to provide the capability to update the network by adding cities. After adding, it should still be able to transmit the message. (Note: We’ll refer to the linked list as the network throughout this document.)

You will include the following cities in your network by default: Los Angeles, Phoenix, Denver, Dallas, Atlanta, & New York

Details: We have defined the class CityNetwork to hold the linked list, and we’ve declared all necessary methods inside it. You will need to complete these methods to implement the linked list functionality (see the starter code).

Implement each city as a struct with (use the starter code)

● a name,

● a pointer connecting it to the next city in the network, and

● a place to store the message being sent. (The message is a string.)

● an integer for the number of messages that have been sent through this city

Program operation: When your program starts, it will display a menu allowing the user to interactively modify your network and send messages. The menu looks like the one shown here:

The user will select the number for the menu option and your program should respond accordingly to that number. Your menu options will support the following functionality:

1. Build Network: This option builds the linked list using the default cities listed above, in the order they are listed. Each city needs to have a name, a pointer to the next city, and a message value, which will initially be an empty string. This option should be selected first to build the network, and can be selected anytime the user wants to rebuild the starting network after adding cities. As part of the Build Network functionality, you should print the name of each city in the network once the network is built in the following format by calling the function for Option #2:

Los Angeles -> Phoenix -> Denver -> Dallas -> Atlanta -> New York -> NULL

Here is a screenshot showing the format that is expected:

2. Print Network Path: This option prints out the linked list in order from the head to the tail by following the next pointer for each city. You should print the name of each city. The function could be very useful to you when debugging your code. The format should be the same as shown above.

There is one space before and after each arrow which is a dash and a >

3. Transmit Message: This option prompts the user to supply a message and a destination, then transmits the message. The message should start at the beginning of the network and end at the city specified. Each city which the message passes through should update its numberMessages variable to count the total number of messages passed through that city.


#> 3
Enter name of the city to receive the message: Atlanta
Enter the message to send: The Broncos game is a blast!
Los Angeles [# messages passed: 1] received: The Broncos game is a blast! Phoenix [# messages passed: 1] received: The Broncos game is a blast!
Denver [# messages passed: 1] received: The Broncos game is a blast! Dallas [# messages passed: 1] received: The Broncos game is a blast! Atlanta [# messages passed: 1] received: The Broncos game is a blast!

Select a numerical option:
+=====Main Menu=========+
1. Build Network
2. Print Network Path
3. Transmit Message
4. Add City
5. Delete City
6. Clear Network
7. Quit
+-----------------------+ #> 3
Enter name of the city to receive the message: New York
Enter the message to send: Moving to east coast
Los Angeles [# messages passed: 2] received: Moving to east coast Phoenix [# messages passed: 2] received: Moving to east coast Denver [# messages passed: 2] received: Moving to east coast Dallas [# messages passed: 2] received: Moving to east coast Atlanta [# messages passed: 2] received: Moving to east coast New York [# messages passed: 1] received: Moving to east coast

4. Add City: This option allows the user to add a new city to the network. If the user selects this option, then they should be prompted for the name of the city and the city that the new city should follow in the network. For ple, if the user wants to add Washington D.C. after Dallas in the network, then the first few cities in the network  would be:

Los Angeles -> Phoenix -> Denver -> Dallas -> Washington D.C. -> ……

If the user wants to add a new city to the head of the network, e.g. replace Los Angeles as the starting city, then they should type First when prompted for the previous city and your code should handle this special case. You do not have to handle the case where the user enters an invalid previous city (we won’t test this).

Here are sample screenshots showing the expected output for the add city functionality when the user selects Add City from the menu.

ple 1:

#> 4
Enter a new city name: Washington D.C.
Enter the previous city name (or First):
adding: Washington D.C. (prev: Dallas)
Los Angeles -> Phoenix -> Denver -> Dallas -> Washington D.C. -> Atlanta -> New York -> NULL

ple 2: Tucson added to the head of the network

#> 4
Enter a new city name: Tuscon
Enter the previous city name (or First):
adding: Tuscon (HEAD)
Tuscon -> Los Angeles -> Phoenix -> Denver -> Dallas -> Washington D.C. -> Atlanta -> New York

5. Delete City: Delete one of the cities in the network. If the user selects this option, then they should be prompted for the name of the city to delete. You do not have to handle the case where the user enters an invalid city.

#> 5
Enter a city name: Dallas
Tuscon -> Los Angeles -> Phoenix -> Denver -> Washington D.C. -> Atlanta -> New York -> NULL

6. Clear Network: Deletes all cities in the network. Inside the deleteEntireNetwork

function, as each node is deleted, print the name of the city being deleted.

#> 6
deleting:  Tuscon deleting: Los Angeles deleting: Phoenix deleting:  Denver deleting: Washington D.C. deleting:  Atlanta deleting: New York Deleted network

7. Quit: This option allows the user to exit the program.

For each of the options presented (except Quit), after the user makes their choice and your code runs for that option, you should re-display the menu to allow the user to select another option.

Program Specifications
● Use the starter code on moodle (HW3-LinkedListNetwork.cpp). Do not modify completed functions, only add your code where indicated.

● Your code needs to be readable, efficient, and accomplish the task provided.

● Make sure your code is commented enough to describe what it is doing. Include a comment block at the top of the .cpp file with your name, project number, and course instructor, and anyone you worked with.

● You must fill in the functions as specified by TODO comments. You do not need any additional functions.

● Consider border cases: what happens when you add or delete cities in the beginning, middle, and end of the list?

Submitting Your Code:
Log into Moodle and go to the  link. It is set up in the quiz format. Follow the instructions on each question to submit all or parts of each project question. You can check your solution to each question by clicking on the “Check” button. Note that you can only submit your  once.

Note: There was confusion on the last project with moodle build errors. You can use the same options moodle does on your machine to get the same errors:

g++ -std=c++11 -Wall -Werror HW3-LinkedListNetwork.cpp

Note: there is no late period on projects! If you miss the deadline or do not do well, you can sign up for an optional grading interview to get up to half the points missed back. There is also an optional extra credit project at the end of the semester you can use to replace one of your  scores.


* Filename:                                           *
* Description:                                        *
* Author:                                             *
* Date:                                               *
#include#include#include#includeusing namespace std;

struct city
string  name;            // name of the city
city *  next;            // pointer to the next city
int     numberMessages;  // how many messages passed through this city
string  message;         // message we are sending accross

class CityNetwork {
// pointer to head of linked list of cities
city* head;
bool isEmpty();
/* NOTE: you will complete all the methods marked
'TODO'. Definitions are below. Careful with the
print statements, moodle expects the output to
match exactly. */
void addCity(city* previous, string cityName); // TODO
void deleteCity(string cityName);              // TODO
void loadDefaultSetup();                       // TODO
city* searchNetwork(string cityName);          // TODO
void deleteEntireNetwork();                    // TODO
void transmitMsg(string receiver, string msg); // TODO
void printPath();                              // TODO

// declarations for UI/menu helper-functions
void displayMenu();
void handleUserInput(CityNetwork& cityNet);

/* Do NOT modify main function */
int main(int argc, char* argv[])
// Object representing our network of cities.
// (Linked list representation is in CityNetwork)
CityNetwork cityNet;

// this will loop until user selects quit option

// quit: clean up.
if (cityNet.isEmpty())
cout << "Path cleaned" << endl; } else { cout << "Error: Path NOT cleaned!" << endl; cityNet.printPath(); } cout << "Goodbye!" << endl; return 0; } /***************************************************************/ /* CityNetwork Methods */ /***************************************************************/ /* TODO: Implement the unfinished methods for CityNetwork. */ /* This class (defined above) uses a linked list of city */ /* structs to store city routes and message counts. */ /***************************************************************/ /* * Purpose: Constructer for empty linked list * @param none * @return none * Do not modify. */ CityNetwork::CityNetwork() { /* finished! do not modify this function. */ head = NULL; } /* * Purpose: Check if list is empty * @return true if empty; else false * Do not modify. */ bool CityNetwork::isEmpty() { /* finished! do not modify this function. */ return (head == NULL); } /* * Purpose: Add a new city to the network * between the city *previous and the city that follows it in the network. * @param previous name of the city that comes before the new city * @param cityName name of the new city * @return none */ void CityNetwork::addCity(city* previous, string cityName) { // TODO: implement this function // required print statements: // print the city name we're adding and city name we're following, e.g. //cout << "adding: " << cityName << " (prev: " << previous->name << ")" << endl; // if adding to front of list, instead print: //cout << "adding: " << cityName << " (HEAD)" << endl; } /* * Purpose: delete the city in the network with the specified name. * @param cityName name of the city to delete in the network * @return none */ void CityNetwork::deleteCity(string cityName) { // TODO: implement this function. // if the city dosn't exist, nothing we can do. // use this output statement cout << "City does not exist." << endl; } /* * Purpose: populates the network with the predetermined cities * @param none * @return none */ void CityNetwork::loadDefaultSetup() { deleteEntireNetwork(); // TODO: implement this function: Add default network cities // e.g., addCity(NULL, "Los Angeles"); } /* * Purpose: Search the network for the specified city and return a pointer to that node * @param cityName name of the city to look for in network * @return pointer to node of cityName, or NULL if not found * @see addCity, deleteCity */ city* CityNetwork::searchNetwork(string cityName) { // TODO: implement this function. // TODO: fix this return statement: should return // a pointer to the city if found. return NULL; } /* * Purpose: deletes all cities in the network starting at the head city. * @param none * @return none */ void CityNetwork::deleteEntireNetwork() { // TODO: implement this function. // required print statement: // print the city name as it's deleted, e.g., //cout << "deleting: " << ptr->name << endl; cout << "Deleted network" << endl; } /* * Purpose: Transmit a message across the network to the * receiver and increment count in each city it passes through * @param receiver name of the city to receive the message * @param message the message to send to the receiver * @return none */ void CityNetwork::transmitMsg(string receiver, string message) { // TODO: implement this function. // if list is empty, print and return if(head == NULL) { cout << "Empty list" << endl; return; } // required print statement: // print the city, count of msgs, and message: // e.g., Denver [# messages passed: 2] received: hi //cout << sender->name << " [# messages passed: " << sender->numberMessages << "] received: " << sender->message << endl; } /* * Purpose: prints the current list nicely * @param ptr head of list */ void CityNetwork::printPath() { cout << "== CURRENT PATH ==" << endl; // TODO: traverse linked list and print path. city* ptr = head; if (head == NULL) { cout << "nothing in path" << endl; } cout << "===" << endl; } /***************************************************************/ /* User Interface Functionality */ /***************************************************************/ /* These functions implement the menu display and handle the */ /* user's menu selection by calling the appropriate */ /* CityNetwork methods. */ /* These functions are complete, DO NOT MODIFY BELOW! */ /***************************************************************/ /* * Purpose: handle the interaction with the user * @param CityNetwork to modify through menu actions * @return None * Do NOT modify */ void handleUserInput(CityNetwork& cityNet) { bool quit = false; string s_input; int input; // loop until the user quits while (!quit) { displayMenu(); // read in input, assuming a number comes in getline(cin, s_input); try { input = stoi(s_input); } catch (exception& e) { // non-numeric input. trigger the default switch case. input = 10; } switch (input) { case 1: // rebuild network cityNet.loadDefaultSetup(); cityNet.printPath(); break; case 2: // print path cityNet.printPath(); break; case 3: // message is read in from stdin // note: 'standard in' is the console by default { string cityReceiver; cout << "Enter name of the city to receive the message: " << endl; getline(cin, cityReceiver); cout << "Enter the message to send: " << endl; string message; getline(cin, message); cityNet.transmitMsg(cityReceiver, message); } break; case 4: // add city { string newCityName; string prevCityName; cout << "Enter a new city name: " << endl; getline(cin, newCityName); cout << "Enter the previous city name (or First): " << endl; getline(cin, prevCityName); // find the node containing prevCity city *tmp = NULL; if(prevCityName !="First") { tmp = cityNet.searchNetwork(prevCityName); } cityNet.addCity(tmp, newCityName); cityNet.printPath(); } break; case 5: // delete city { string city; cout << "Enter a city name: " << endl; getline(cin, city); cityNet.deleteCity(city); cityNet.printPath(); } break; case 6: // delete network cityNet.deleteEntireNetwork(); break; case 7: // quit quit = true; cout << "Quitting... cleaning up path: " << endl; break; default: // invalid input cout << "Invalid Input" << endl; break; } } } /* * Purpose: displays a menu with options * Do not modify. */ void displayMenu() { cout << endl; cout << "Select a numerical option:" << endl; cout << "+=====Main Menu=========+" << endl; cout << " 1. Build Network " << endl; cout << " 2. Print Network Path " << endl; cout << " 3. Transmit Message " << endl; cout << " 4. Add City " << endl; cout << " 5. Delete City " << endl; cout << " 6. Clear Network " << endl; cout << " 7. Quit " << endl; cout << "+-----------------------+" << endl; cout << "#> ";