Lab 6
                    Working with Files and Objects

  Introduction
  ============
  You've been working very hard!  In this lab, we will step back a
  little and work through some examples of using file streams and
  objects.  Not to worry though, I promise this will still be a
  challenging and rewarding lead in to the next leg of the journey!



  Lab 6.1 (Guided)  Selling more than 3 things
  ============================================
  The owners of Trillium Inc. have decided to replace their old cash
  register system.  Their old system was severely limited, so they are
  a bit wary of programmers.  Also, their cashiers have complained
  that the old system is too complicated to use.  They want something
  simple and menu driven.  Finally, the owners have decided that it
  would be nice if the cash register could keep a record of its
  transactions.  You know, that way they can track sales and make sure
  they have the right amount of money on hand.

  For the first part of this, we are going to create a simple menu
  system for the register.  It will have 2 modes, transaction entry
  and journal review.  We will be storing the cash register history in
  a file.  The first step is to produce a stub of this program in
  order to test out the menu system.  Enter and execute the following
  code, come back when you have it running.


  --begin register.cpp --
  #include <iostream>
  #include <iomanip>
  #include <fstream>
  #include <cctype>
  
  
  using namespace std;

  //function prototypes
  int menu();
  void newTransaction();
  void writeLineItem(string item, int qty, double cost)
  void endTransaction();
  void readReceipts();
  
  
  int
  main(void) {
    int choice;
  
    //drive the menu
    do {
      choice = menu();  //get the choice
  
      switch(choice) {
      case 1:  //new transaction
        newTransaction();
        break;
  
      case 2: //print journal
        readReceipts();
        break;
      }
    } while(choice !=3);
        
    return 0;
  }
  
  
  // displays the menu and returns a valid result 
  int
  menu() {
    int choice;
  
    cout << "   Cash Register Menu" << endl;
    do {
      cout << "1.  Enter a new transaction." << endl;
      cout << "2.  Review journal of transactions." << endl;
      cout << "3.  Exit" << endl;
      cout << endl << "Choice? ";
  
  
      //discard non integer input
      while (!isdigit(cin.peek())) cin.get();
  
      cin >> choice;
  
      if(choice < 1 || choice > 3) {
        cout << "Invalid selection.  Please try again." << endl;
      }
    } while(choice < 1 || choice > 3);
  
    return choice;
  }
    
  
  void
  newTransaction() {
    cout << "newTransaction" << endl;
  }
  
  
  void
  writeLineItem(string item, int qty, double cost) {
    cout << "writeLineItem" << endl;
  }

  
  void
  endTransaction() {
    cout << "endTransaction" << endl;
  }
  
  
  void
  readReceipts() {
    cout << "readReceipts" << endl;
  }
  
  --end register.cpp --


  Notice how all the above functions are stubs.  This allows us to
  test the program and see what functions are getting executed.  The
  next step is to implement the cashier's interface.  What the
  cashiers have decided is that they want to enter an item, the
  quantity of the item, and its cost.  They want to repeat this until
  they enter a blank item.  Then they want a simple display indicating
  the total amount due on the receipt.  Also, if we keep in mind that
  we want to write all this to a journal, we can go ahead and call our
  writeLineItem function as well as our endTransaction function.  

  We do all this in the newTransaction function.  Modify
  newTransaction so that it reads as follows:


  void
  newTransaction() {
    string item;
    int qty;
    double cost;
    double total = 0.0;
    
    //go until we get an empty item
    do {
      //clear out cin
      cin.clear(); cin.ignore(1000, '\n');
      
      cout << "Item (blank to end): ";
      getline(cin, item);
      if(!item.length()) continue;
      cout << "Qty: ";
      cin >> qty;
      cout << "Price: ";
      cin >> cost;
  
      //add to the journal
      writeLineItem(item, qty, cost);
  
      //add to the total
      total += qty * cost;
    } while(item.length());
  
    cout << "Total Due: $" << fixed << setprecision(2) << total << endl;
  
    //mark the end of the transaction
    endTransaction();
  }


  Test your program again to make sure it is working.

  We now turn our attention to the journal file.  We have to declare
  the format that we are going to store transactions in.  Because item
  names can contain spaces, we will put each field on a line by
  itself.  Thus the format goes:

    item name
    quantity
    cost

  With a blank line separating transactions.  Because we are
  journaling, we want to open the file in append mode.  The two key
  operations are "writeLineItem" and "endTransaction".  Modify these
  two functions so they read as below:

  void
  writeLineItem(string item, int qty, double cost) {
    ofstream file;  //the journal file
  
    //append a single item to the file, one field at a time
    file.open("registerTape", ios::app);
    file << item << endl;
    file << qty << endl;
    file << cost << endl;
    file.close();
  }

  void
  endTransaction() {
    ofstream file;  //the journal file
  
    //append a single blank line to the file.  This ends the transaction.
    file.open("registerTape", ios::app);
    file << endl;
    file.close();
  }

  Test this program out now.  Note that it creates a file named
  "registerTape" in your directory.  cat registerTape and verify that
  this writes the correct format.  You should enter a few transactions
  using your program to test it.

  Now we only need to provide a way of running the reports. To do
  this, we start with the following modification:

  void
  readReceipts() {
    ifstream file;  //the journal file;
    string item;
    int qty;
    double cost, lineCost;
    double total = 0.0;
  
    //open the file and read to the end
    file.open("registerTape");
    while(!file.eof()) {
      //get the item
      getline(file, item);
  
      //handle break in transactions
      if(!item.length()){
        //display the transaction total and reset
        if(total > 0)
          cout << setw(32) << total << endl << endl;
        total = 0.0;
        continue;
      }
  
      //get the other fields
      file >> qty >> cost;
  
      //consume newline
      if(file.peek() == '\n') file.get();
  
      //do a little math stuff
      lineCost = qty * cost;
      total += lineCost;
  
      //print a user friendly display
      cout << fixed << setprecision(2)
           << setw(10) << item << ' ' << setw(5) << qty << ' '
           << setw(7)  << cost << ' ' << setw(7) << lineCost << endl;
    }
    file.close();
  }
  

  Run your program a few times, enter some transactions, and verify
  that they show up in the reports.

  Now as a final exercise, cleanup the output of readReceipts to make
  it look better.  Add some headers and some dollar signs.  This is a
  subjective thing, so I want you to be creative.  Have fun practicing
  your formatting skills and make a display you can be proud of.

  When you are done, create a script file containing your complete
  code, your run, and a cat of your registerTape file.


  Lab 6.2  Computing Your Grade
  =============================
  Imagine, for a moment, that you are in a CS class who's final grade
  is computed by means of weighted averages divided into the following
  categories: 

    Exams: 40%
    Guided Lab Assignments: 10%
    Self Completed Lab Assignments: 30%
    Assignments: 20%

  Given your present circumstances, you shouldn't have to tax your
  imagination too heavily!  Now, suppose that you want to keep track
  of your grade.  A great way to do this would be with a program which
  keeps records in a file.  Since that is the topic of this lab, I
  think you can see where we are headed!

  So now, here's your task.  You want to design and implement a
  program which does the following:

    1. Presents the user with the choice of entering a new grade or
       reviewing old grades.

    2. Stores the grades in a single file.

    3. Shows a grade report listing all of your scores (along with the
       category of each) and displays the averages for each category,
       and the weighted final average.

  The design of the interface and the file are completely up to you
  this time!  Be sure to include a description of your file format in
  the pseudocode.  Also, include examples of what your user interface
  will look like.


  HINTS:  
    - enum is your friend.  There are only so many categories.
    - You can use a similar strategy to that which was developed in the
      guided part of lab 6.