CSCI 161 lab exercise 3: circular buffers

The exercise will be marked out of 10, and is worth 5% of your total grade.

Late submissions will be penalized 2.5 marks per day late or part thereof.

Exercise details:

You will be implementing a CircularBuffer class and a program using it, with both conforming to the definitions in the labex3.h header file below.

All of your code is to be in a single file, named labex3.C, which includes and uses the labex3.h file.

I will be using my own copy of labex3.h for compiling and testing your code, and deriving a class from your CircularBuffer class, so make sure it conforms exactly to the specifications.

The CircularBuffer class

• The buffer class is to be implemented to conform to the header file supplied, following the circular buffer concepts discussed in lectures and labs. You will not receive credit for the assignment if you alter the header file or use a different implementation approach.

  The program that uses it

• The main routine must ask the user how large an array they wish to use, read in the value, and call the CircularBuffer constructor appropriately.
• It must then repeat the following cycle until the user decides to quit:
  • Ask them to enter a command (the only valid options are the ones listed in the enumerated type)
  • Read in the command
  • If the command is invalid then display an error message
  • If the command is to enqueue then prompt the user to enter a line of text, read it in, enqeue it, and tell the user whether it was successful or not
  • If the command is to dequeue then attempt to dequeue a line of text, if successful then display it, otherwise display an error message
  • If the command is to print then call the print method to do so.
  
  Following that command cycle is a required part of the specifications: do not alter or augment the sequence or the commands used!

//  labex3.h 
#ifndef LABEX3_H
#define LABEX3_H
#include <string>
using namespace std;

// implement a queue using a circular buffer
class CircularBuffer {
   protected:
      int bufSize;    // the size of the array
      int itemCount;  // the number of currently enqueued items
      int frontIndx;  // the array position of the front item
      int backIndx;   // the array position of the back item
      string* buffer; // the allocated array of strings
      
   public:
      // the default size of the array
      static const int DefaultSize = 5;

      // allocates an array of the specified size,
      //    and initializes all the protected fields
      CircularBuffer(int size = DefaultSize);

      // deallocate the array
      ~CircularBuffer();

      // add the string to the back of the queue,
      //     adjusting back and wrapping around if necessary
      // return true if successful, false otherwise
      bool enqueue(string s);

      // copy out the string from the front of the queue,
      //     adjusting front and wrapping around if necessary
      // return true if successful, false otherwise
      bool dequeue(string &s);

      // print the items currently in the queue,
      //    from front to back,
      // displaying one string per line
      void print();
};

// all text strings entered by the user will be limited
//     to this size PLUS a null terminator
const int MaxTextLen = 255;

// the permitted user commands for the application 
enum Command { 
   QuitCmd = 'Q',    // exit the program
   EnqueCmd = 'E',   // enter a text string and enqueue it
   DequeCmd = 'D',   // dequeue a text string and display it
   PrintCmd = 'P'    // print the currently enqueued items
                     //    from the (current) front to back
};

#endif

Recommended development sequence As always, I advise you follow a well-thought out sequence of development steps in completing the exercise. The details are being left up to you for this lab.

Submission mechanism

All the code must be in a single file this time, labex3.C,
(correct spelling and capitalization is essential for the submission to work correctly).

To submit the assignment, cd to the directory that contains your labex3.C file and type the following command:

   /home/faculty/wesselsd/bin/submit  161  labex3.C

Marking guidelines:

Marks will be based on:

• The program must compile cleanly (no warnings or errors) using the g++ compiler (with the -Wall option) on the csci lab server (csci.viu.ca, a.k.a. csci.viu.ca) and run without crashing on that server.
• Your circular buffer implementation must be robust, and follow the circular buffer approaches discussed in the labs and lectures.
• Your main routine must follow the input/output specifications described above: no more, and no less.
• You must not alter labex3.h, and must use it appropriately in labex3.C
• You must adhere to the standards listed below
• The code itself must be of good quality - i.e. the code is clear, readable, easy to understand, easy to modify.

Code standards:

The submission must follow the code standards for labex2,