CP1300 C++ Classes

Content

• Write a program that reads in two people's names and ages, and writes them out in alphabetical order by last name.
  • Inputs: Name1, Age1, Name2, Age2.
  • Outputs: Name and Age pairs, ordered by name.
  • Design

              Read Name1, Age1
              Read Name2, Age2
              If Name1 > Name2
                  Swap Name1 and Name2
                  Swap Age1 and Age2
              Output Name1 and Age1
              Output Name2 and Age2
              

• Using normal C strings the following is about as good as it gets
  • mystrlib.h - My string library header
  • mystrlib.cpp - My string library implementation
  • NameAgeTwoV5.cpp - The NameAge program, version 5

• Problems with the C strings implementation
  • Lack of security on manipulation of the data. Data can be changed by mechanisms other than the ADT operations we define, e.g., by
    • SetEndInMiddle.cpp - Setting a character to '\0'
    • DeleteEnd.cpp - Overwriting the '\0' character (p.287).
  • Parameter passed to every string manipulation function. See mystrlib.h - My string library header, for example.

• Solution: Encapsulate ADTs using C++ classes (p.287)
  • Gives a logical view of the data. No details of implementation.
  • Clients of a class can only used the defined operations on instances of the class. (p.263)
  • The operations are associated with the instances, so data is not a parameter. This is somewhat like a struct with functions as fields.
  • Where normally functions are considered as idependent entities that process independently existing data, using classes places the data at the centre with the operations (functions) surrounding them as access mechanisms.

• Declaring a string class (p.288)
  • mystrclass.h - My string class header
  • General format and the components (p.289)
  • Directives
  • Constants
  • public and private parts
  • Default and initial value constructor function declarations
  • Member function declarations
  • Data definitions

• Implementing a string class (p.290)
  • mystrclass.cpp - My string class implementation
  • Default and initial value constructor functions
  • Member functions
  • Access to this instance's data
  • Access to other instance's data

• Using instances of a string class (p.292)
  • ReadAge.cpp - Reading an age
  • Initialization
  • Assignment
  • Calling member functions

• NameAgeTwoCV1.cpp - The NameAge program, class version 1

• Another version of a string class
  • strlib.h - Header file (p.288)
    • Copy constructor function declaration
  • strlib.cpp - Implementation file (p.291)
    • Copy constructor function
  • ExtractLower.cpp - Using the class

• Array of integers example

  Write a program that stores the integer marks of a student for several items of assessment, each of equal value. The program outputs the total and average mark.

  • Smart class solution
    • smartintarrayclass.h - Smart integer array class header
    • smartintarrayclass.cpp - Smart integer array class implementation
    • MarksClass.cpp - Marks program (Class)

• Object Oriented Programming - OOP (p.305)
  • The problem of Software Maintenance (p.305)
  • Reuse of Software (p.306)
  • Basic Ideas and Terminology of OOP (p.306)
    • Objects, attributes, and behaviours
    • Messages
    • Servers and Clients
    • Senders and Receivers
    • Inheritance
    • Polymorphism
  • OOP in C++
    • Objects (servers) = instances of classes
    • Attributes = Values stored in the data members
    • Behaviours = Activities of functions
    • Clients = User code
    • Messages = Calls to member functions
    • Senders = User code and member functions
    • Receivers = Member functions
    • Inheritance = Inheritance
    • Polymorphism = Overloading
  • ADTs via OOP
    

    An Abstract Data Type (ADT) consists of a set of values, a defined set of properties of these values, and a set of operations for processing the values.

    • Set of values = Attributes = Values stored in the data members
    • Properties = As defined by the Attributes
    • Operations = Behaviours = Activities of functions
  • OOP can be used for more than implementation of ADTs.

• A Bank Account Class (p.307)
  • account.h - Bank account class header file (p.309)
  • account.cpp -Bank account class implementation file (p.310)
  • bankdriv.cpp -Bank account program (p.311)

• A Person Class
  • mystrclass.h - My string class header
  • mystrclass.cpp - My string class implementation
  • nameageclass.h - Name and age class header
  • nameageclass.cpp - Name and age class implementation

• NameAgeTwoCV2.cpp - The NameAge program, class version 2
  • Consider the object structure (it's nested! (or is it?))

• Functions can return instances
  • Rational number ADT
    • Values are pairs of integers, a numerator and a denominator
    • Numerator has property of being a positive or negative integer
    • Denominator has property of being a natural number
    • Operations include Set, Read, Write, Add, Subtract, Multiply, Divide.
  • rationalclass.h
  • rationalclass.cpp
  • UseRationals.cpp

• Classes
• Class strings
• OOP

Tutorial Questions

• Use of mystrclass
• Building a class for complex numbers
• Adding an initial value constructor to the complex class

Exam style questions

1. Programs may be monolithic, may be organized with libraries, or may use classes.
   • What is the major problem with using libraries as a way of organizing code?
   • What is meant by encapsulation, and how can it overcome this problem?
   • How does C++ implement encapsulation?
2. Given the following class implementation file integer_store.cpp, provide the class header file integer_store.h.

   #include "boolean.h"
   #include "integer_store.h"
   //-------------------------------------------------------------
   integer_store::integer_store(void) {
   
   Clear();
   }
   //-------------------------------------------------------------
   integer_store::integer_store(int Value) {
   
   Store(Value);
   }
   //-------------------------------------------------------------
   void integer_store::Store(int Value) {
   
   ValuedStored = TRUE;
   TheValue = Value;
   }
   //-------------------------------------------------------------
   void integer_store::Clear(void) {
   
   ValuedStored = FALSE;
   }
   //-------------------------------------------------------------
   boolean integer_store::Retrieve(int &Value) {
   
   if (ValueStored) {
       Value = TheValue;
       return(TRUE);
       }
   else return(FALSE);
   }
   //-------------------------------------------------------------
   

3. In the context of Object Oriented Programming, explain how the following are implemented in C++:
   • Objects
   • Attributes
   • Behaviours
   • Messages
4. Write the header and implementation file for a class that stores a person's name as their first name initial and complete family name. Include a default constructor that initializes the name to J. Citizen, an initial value constructor, and a member function that writes out the name.