OBJECTIVES
1.	Create, add to, delete from, and work with a stack implemented as a linked list
2.	Create, add to, delete from, and work with a queue implemented as an array

Stacks and Queues are both data structures that can be implemented using either an array or a linked list. You will gain practice with each of these in the following two mini-projects. The first is to build a simple calculator using a linked list stack and the second is to simulate a multi-process publisher-subscriber problem using a circular array based queue.

Stack Calculator

During the 70s and 80s, Hewlett-Packard used the so-called Reverse Polish Notation (RPN) in all their calculators. The notation refers to the way that binary operations are processed. Rather than the standard infix notation 1 + 1, RPN, or postfix notation, is written 1 1 +. While it may look backward at first, it is actually less ambiguous to write operations this way and it lends itself to an elegant implementation with a stack. As numbers (operands) are entered to the calculator, they are pushed onto a stack. When an operator, e.g. +, is entered, the top two elements on the stack are popped, added, and the result is pushed back to the stack. Note that you can load the stack with more than two operands; for example, entering the following sequence of inputs 1.5, 2, 4, +, + will add 4+2, push the result, 6, to the stack, then add 6+1.5, and push 7.5 to the stack.

Instruction	Stack
#> 1.5
#> 2

CSCI 2270 Data Structures

Instructors: Zagrodzki, Ashraf, Trivedi

Due Sunday, March 1, 11:59PM

#> 4
#> +
#> +

Similarly, the input sequence 2,3,4, *, 3, +, + performs the product 4*3, then the sum 3+12, then the sum 15+2 and the resulting stack will have one item: 17.

Instruction	Stack
#> 2
#> 3
#> 4
#> *
#> 3

Due Monday, June 29, 11:59PM MDT

#> +
#> +

Publisher-Subscriber Problem

In parallel computing, the publisher-subscriber problem describes a simple synchronization task involving two processes; a publisher, which generates data, and a subscriber, which processes data. The problem is that they may work at different speeds, causing one process to wait for the other which is very inefficient. We can solve this problem by creating a data buffer in the form of a queue. When the publisher generates some data it pushes it to the queue. The subscriber dequeues data and processes it as it comes in. You will simulate this interaction (without parallelism of course) using a circular queue.

Starter Code on Moodle

Do not modify the provided header files. You are provided with skeletons of your driver programs (Stack CalculatorDriver.cpp, PubSubDriver.cpp ) which you need to complete and submit on Moodle. Write one corresponding C++ file for each header file that implements all of the class methods (a few of the getter functions are defined already, so you dont have to implement them). The names of these files are below:

• Provided Starter Code:

Stack Calculator files

StackCalculator.hpp (DO NOT MODIFY)

StackCalculatorDriver.cpp (TODO #1)

Publisher-Subscriber files

PubSub.hpp (DO NOT MODIFY)

PubSubDriver.cpp (TODO #2) IMPORTANT: Files you need to create:

StackCalculator.cpp (TODO #3)

PubSub.cpp (TODO #4)

StackCalculator Class

You will build a Stack calculator that can perform addition and multiplication on floating point numbers. This class utilizes the functionality of a linked list stack, which employs the following struct (included in StackCalculator.hpp )

struct{ Op floatOp* next; num; };

Implement the StackCalculator class according to the following specifications

Op* head

• Points to the top of the stack (first node in the linked list). This is defined in the header file.

StackCalculator()

• Constructorset the head pointer to NULL

~StackCalculator()

• Destructorpop everything off the stack and set head to NULL.

bool isEmpty()

• Returns true if the stack is empty (i.e. head is NULL), false otherwise

void push(float num)

• Insert a new node with num onto the top of the stack (beginning of linked list)

void pop()

If the stack is empty, print Stack empty, cannot pop an item. and return. Otherwise delete the top most item from the stack

Op* peek()

• If the stack is empty, print Stack empty, cannot peek. and return NULL. Otherwise, return a pointer to the top of the stack bool calculate(std::string symbol )
• Perform the arithmetic operation symbol, which will be either + or *, on the top 2 numbers in the stack. The return value indicates whether the operation was carried out successfully
• If symbol is not + or *, print err: invalid operation and return false
• Store the floats from the top two elements in the stack in local variables and pop

Before getting each element, make sure that the stack is not empty. If it is empty, print err: not enough operands and return false

If you pop the first element, and notice that the list is empty prior to getting the next element, print the error message, push the first element back to the stack (use push function), and return false

• Perform the arithmetic operation symbol on those two elements and push the result to the stack

**Important

• use NULL, and not nullptr.
• make sure the prompt #> (without a newline at the end of prompt) is printed at every input of float or an operand.
• Only = marks the end of expression. Till the end of expression is reached, the code is expected to: consume input, print error message if any, ignore the said erroneous input, and continue onto the next available input.

StackCalculator main driver file

• Create a stack by instantiating an StackCalculator object
• Prompt the user to enter the operators and operands using the print statement, Enter the operators and operands (+, *) in a postfix format
• Read user inputs (Tip: use getline for all inputs which is shown in the starter code) until = is entered. If the input is a number (isNumber function provided in starter code) then push it onto the stack, else, call the calculate function on the input When your program reads =:
  • If the stack is empty print No operands: Nothing to evaluate and return
  • If the expression is invalid print Invalid expression and return. An expression is considered valid if there is exactly one item left on the stack. (Hint: pop the last item and check if the stack is empty)
  • Otherwise, print the result of the expression (for floating numbers limit the precision to 4 decimals)

Below are some sample outputs

SAMPLE OUTPUT 1Enter the operators and operands (+, *) in a postfix format #> 2.5 #> 3 #> + #> 2.4 #> * #> =13.2

SAMPLE OUTPUT 2Enter the operators and operands (+, *) in a postfix format #> 15 #> 25 #> * #> 30 #> =Invalid expression

ProducerConsumer Class

**Beware of edge cases that arise from the array being circular**

In this class you will build a queue using the circular array implementation. Implement the methods of ProducerConsumer according to the following specifications.

std::string queue[SIZE]

• A circular queue of strings in the form of an array. SIZE is initialized to a default value of 20 in hpp

int queueFront

• Index in the array that keeps track of the front item

int queueEnd

• Index in the array that keeps track of the first available empty space (in case the queue is full, queueEnd points to queueFront).

ProducerConsumer()

• ConstructorSet queueFront and queueEnd to 0

bool isEmpty()

• Return true if the queue is empty, false otherwise

bool isFull()

• Return true if the queue is full, false otherwise

void enqueue(std::string item)

If the queue is not full, then add the item to the end of the queue and modify queueFront and/or queueEnd if appropriate, else print Queue full, cannot add new item

void dequeue()

• Remove the first item from the queue if the queue is not empty and modify queueFront and/or queueEnd if appropriate. Otherwise print Queue empty, cannot dequeue an item

int queueSize()

• Return the number of items in the queue.

std::string peek()

If the queue is empty then print Queue empty, cannot peek and return an empty string.

Otherwise, return the first item in the queue.

PXEOLVKHU6XEVFULEHU main driver file

Your program will start by displaying a menu by calling the menu() function which is included in the provided skeleton code. The user will select an option from the menu to decide upon what the program will do, after which the menu will be displayed again. Below are the specifics of the menu (Tip: use getline for all inputs, the example is shown in the starter code.)

Option 1: Publisher (Publish items to the queue) This is an enqueue operation

• This option prompts the user to enter the number of items being produced using the below print statement

cout << Enter the number of items to be published: << endl;

• Then prompt the user to enter each item using the below print statement

cout << Item << <ITEM_NO> << : << endl;

• Produce (enqueue) all the items into the queue

Option 2: Subscriber (Retrieve items from the queue) This is a dequeue operation

• This option prompts the user to enter the number of items being consumed using the below print statement

cout << Enter the number of items to be retrieved: << endl;

• Consume (dequeue ) items from the queue. If the number of items to be consumed is greater than the total number of items in the queue, then consume (dequeue ) all the available items in the queue and notify the user with a below statement

cout<< No more items to retrieve from queue << endl;

This message should never be printed more than once.

• For each item consumed, print the following

cout << Retrieved: << item << endl;

where item is the string you are dequeuing.

Option 3: Return the queue size and exit

• This option prompts the user to return the number of items in the queue using the below print statement, before exiting the program.

cout << Number of items in the queue: <item_count> ;

Below is a sample output

*-*

Choose an option:

1. Publisher (Publish items to the queue)
2. Subscriber (Retrieve items from the queue)
3. Return the queue size and exit

*-*

1

Enter the number of items to be published:

3

Item1

Honey

Item2

Bread

Item3

Butter

*-*

Instructors: Ashraf, Godley Due Monday, June 29 11:59PM

Choose an option: 1. Publisher (Publish items to the queue)2. Subscriber (Retrieve items from the queue)3. Return the queue size and exit *-* 2Enter the number of items to be retrieved: 2Retrieved: Honey Retrieved: Bread *-* Choose an option:1. Publisher (Publish items to the queue)2. Subscriber (Retrieve items from the queue)3. Return the queue size and exit *-* 3Number of items in the queue:1