An Overview of Object-Oriented Programming and C

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An Overview of Object-Oriented Programming and C
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• Object-Oriented Programming Using C
• Second Edition

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Objectives
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• In this chapter, you will learn
• About the task of programming
• About programming universals
• About procedural programming
• About object-oriented programming
• About the C programming environment
• How to create a main() function

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Objectives
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• In this chapter, you will learn
• How to work with variables and the const
  qualifier
• How to create comments
• How to use libraries and preprocessor directives
• How to use cout and cin
• How to work with classes

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The Task of Programming
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• Programming a computer involves writing
  instructions that enable a computer to carry out
  a single task or a group of tasks
• A computer programming language requires learning
  both vocabulary and syntax
• Programmers use many different programming
  languages, including BASIC, Pascal, COBOL, RPG,
  and C
• The rules of any language make up its syntax
• Machine language is the language that computers
  can understand it consists of 1s and 0s

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The Task of Programming
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• A translator (called either a compiler or an
  interpreter) checks your program for syntax
  errors
• A logical error occurs when you use a statement
  that, although syntactically correct, doesnt do
  what you intended
• You run a program by issuing a command to execute
  the program statements
• You test a program by using sample data to
  determine whether the program results are correct

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Programming Universals
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• All programming languages provide methods for
  directing output to a desired object, such as a
  monitor screen, printer or file
• Similarly, all programming languages provide
  methods for sending input into the computer
  program so that it can be manipulated
• In addition, all programming languages provide
  for naming locations in computer memory
• These locations commonly are called variables (or
  attributes)

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Programming Universals
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• Ideally, variables have meaningful names,
  although no programming language actually
  requires that they meet this standard
• A variable may have only one value at a time, but
  it is the ability of memory variables to change
  in value that makes computers and programming
  worthwhile
• In many computer programming languages, including
  C, variables must be explicitly declared, or
  given a data type as well as a name, before they
  can be used

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Programming Universals
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• The type determines what kind of values may be
  stored in a variable
• Most computer languages allow at least two types
  one for numbers and one for characters
• Numeric variables hold values like 13 or -6
• Character variables hold values like A or
• Many languages include even more specialized
  types, such as integer (for storing whole
  numbers) or floating point (for storing numbers
  with decimal places)

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Procedural Programming
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• Procedural programs consist of a series of steps
  or procedures that take place one after the other
• The programmer determines the exact conditions
  under which a procedure takes place, how often it
  takes place, and when the program stops
• Programmers write procedural programs in many
  programming languages, such as COBOL, BASIC,
  FORTRAN, and RPG
• You can also write procedural programs in C

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Early Procedural Programs
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• When programming languages were first used, the
  programmers job was to break a task into small,
  specific steps
• Each step was then coded in an appropriate
  language
• Three basic control structures are used in
  procedural programming
• In the first structure, a sequence, program steps
  execute one after another, without interruption

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Early Procedural Programs
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• Procedural programs also can include a second
  control structure called selection, which you use
  to perform different tasks based on a condition

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Early Procedural Programs
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• The third control structure used in computer
  programs is the loop
• some programmers call the loop structure a
  repetition or iteration structure

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Adding a Loop to a Simple Procedural Billing
Program
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Modularity and Abstraction
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• Programming in the oldest procedural languages
  had two major disadvantages
• The programming process involved so much detail
  that the programmer (and any person reading the
  program) lost sight of the big picture
• Similar statements required in various parts of
  the program had to be rewritten in more than one
  place
• Writing programs became easier when programming
  languages began to allow the programmer to write
  methods
• Using methods allows programmers to group
  statements together into modules or routines

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Modularity and Abstraction
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The Procedural Billing Program Containing Several
Module Calls
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Encapsulation
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• Modules or procedures act somewhat like
  relatively autonomous mini-programs
• Not only can modular routines contain their own
  sets of instructions, but most programming
  languages allow them to contain their own
  variables as well
• The variables and instructions within a module
  are hidden and contained that is
  encapsulatedwhich helps to make the module
  independent of all other modules, and therefore
  reusable

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Object-Oriented Programming
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• Object-oriented programming requires a different
  way of thinking and adds several new concepts to
  programming
• You analyze the objects with which you are
  workingboth the attributes of those objects and
  the tasks that need to be performed with and on
  those objects
• You pass messages to objects, requesting the
  objects to take action
• The same message works differently when applied
  to the various objects

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Object-Oriented Programming
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• A method can work appropriately with different
  types of data it receives, without the need for
  separate method names
• Objects can share or inherit traits of previously
  created objects, thereby reducing the time it
  takes to create new objects
• Information hiding is more complete than in
  procedural programs

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Object-Oriented Programming
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• The basic principles behind using object-oriented
  programming techniques involve
• Objects
• Classes
• Inheritance
• Polymorphism

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Objects and Classes
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• An object is any thing
• A class consists of a category of things
• An object is a specific item that belongs to a
  class it is called an instance of a class
• A class defines the characteristics of its
  objects and the methods that can be applied to
  its objects
• It is conventional, but not required, to begin
  object names with a lowercase letter, and to
  begin class names with an uppercase letter

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Inheritance
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• The concept of using classes provides a useful
  way to organize objects it is especially useful
  because classes are reusable or extensible
• You can create new classes that extend or are
  descendants of existing classes
• The descendent classes can inherit all the
  attributes of the original (or parent) class, or
  they can override inappropriate attributes

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Polymorphism
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• Programming modules might occasionally need to
  change the way they operate depending on the
  context
• Object-oriented programs use polymorphism to
  carry out the same operation in a manner
  customized to the object
• Without polymorphism you would have to use a
  separate module or method name for a method that
  multiplies two numbers and one that multiplies
  three numbers
• Without polymorphism you would have to create
  separate module names for a method that cleans a
  Dish object, one that cleans a Car object, and
  one that cleans a Baby object

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Getting Started in the C Programming Environment
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• Depending on your C installation, you can
  access the compiler by clicking an icon,
  selecting from a menu, or typing a command
• The main work area in any C programming
  environment is the editor
• An editor is a simplified version of a word
  processor in which you type your program
  statements, or source code
• After you enter the source code for a program,
  you must compile the program

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Getting Started in the C Programming Environment
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• When you compile, the code you have written is
  transformed into machine languagethe language
  that the computer can understand
• The output from the compilation is object code
• When a C program is compiled, a file is created
  that has the same filename as the source code,
  but has the extension .obj
• A runnable, or executable, program needs the
  object code as well as code from any outside
  sources (other files) to which it refers

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Getting Started in the C Programming Environment
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• The process of integrating these outside
  references is called linking
• An executable file contains the same filename as
  the source code and the object code, but carries
  the extension .exe to distinguish it as a program
• When you compile a C program, error messages
  and/or warnings might appear
• A C program with errors will not execute you
  must eliminate all error messages before you can
  run the program

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Creating a main( ) Function
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• C programs consist of modules called functions
• Every statement within every C program is
  contained in a function
• Every function consists of two parts
• A function header is the initial line of code in
  a C which always has three parts
• Return type of the function
• Name of the function
• Types and names of any variables enclosed in
  parentheses, and which the function receives
• A function body

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Creating a main( ) Function
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• A C program may contain many functions, but
  every C program contains at least one function,
  and that function is called main( )
• If the main function does not pass values to
  other programs or receives values from outside
  the program, then main( ) receives and returns a
  void type
• The body of every function in a C program is
  contained in curly braces, also known as curly
  brackets

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Creating a main( ) Function
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• Every complete C statement ends with a
  semicolon
• Often several statements must be grouped
  together, as when several statements must occur
  in a loop
• In such a case, the statements have their own set
  of opening and closing braces within the main
  braces, forming a block

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Working with Variables
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• In C, you must name and give a type to
  variables (sometimes called identifiers) before
  you can use them
• Names of C variables can include letters,
  numbers, and underscores, but must begin with a
  letter or underscore
• No spaces or other special characters are allowed
  within a C variable name
• Every programming language contains a few
  vocabulary words, or keywords, that you need in
  order to use the language

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Common C Keywords
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Working with Variables
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• A C keyword cannot be used as a variable name
• Each named variable must have a type
• C supports three simple types
• Integer Floating point Character
• An integer is a whole number, either positive or
  negative
• An integer value may be stored in an integer
  variable declared with the keyword int
• You can also declare an integer variable using
  short int and long int

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Working with Variables
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• Real or floating-point numbers are numbers that
  include decimal positions, such as 98.6,
  1000.00002, and -3.85
• They may be stored in variables with type float,
  double, and long double
• Characters may be stored in variables declared
  with the keyword char
• A character may hold any single symbol in the
  ASCII character set
• Often it contains a letter of the alphabet, but
  it could include a space, digit, punctuation
  mark, arithmetic symbol, or other special symbol

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Working with Variables
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• In C, a character value is always expressed in
  single quotes, such as A or
• To declare a variable, you list its type and its
  name
• In addition, a variable declaration is a C
  statement, so it must end with a semicolon
• If you write a function that contains variables
  of diverse types, each variable must be declared
  in a statement of its own
• If you want to declare two or more variables of
  the same type, you may declare them in the same
  statement

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Working with Variables
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• Explicitly stating the value of a variable is
  called assignment, and is achieved with the
  assignment operator
• The variable finalScore is declared and assigned
  a value at the same time
• Assigning a value to a variable upon creation is
  often referred to as initializing the variable

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The const Qualifier
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• A variable that does not change in a program
  should not be declared as a variable
• Instead, it should be a constant
• The statement const double MINIMUM_WAGE 5.75
  declares a constant named MINIMUM_WAGE that can
  be used like a variable, but cannot be changed
  during a program

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Creating Comments
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• Comments are statements that do not affect the
  compiling or running of a program
• Comments are simply explanatory remarks that the
  programmer includes in a program to clarify what
  is taking place
• These remarks are useful to later program users
  because they might help explain the intent of a
  particular statement or the purpose of the entire
  program
• C supports both line comments and block comments

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Creating Comments
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• A line comment begins with two slashes (//) and
  continues to the end of the line on which it is
  placed
• A block comment begins with a single slash and an
  asterisk (/) and ends with an asterisk and a
  slash (/) it might be contained on a single
  line or continued across many lines

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Using Libraries and Preprocessor Directives
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• Header files are files that contain predefined
  values and routines, such as squrt( )
• Their filenames usually end in .h
• In order for your C program to use these
  predefined routines, you must include a
  preprocessor directive, a statement that tells
  the compiler what to do before compiling the
  program
• In C, all preprocessor directives begin with a
  pound sign (), which is also called an octothorp
• The include preprocessor directive tells the
  compiler to include a file as part of the
  finished product

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C Output
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• C provides several objects for producing output
• The simplest object is called cout, pronounced
  see out
• When contained in a complete C program, the
  statement coutltltHi there places the phrase Hi
  there on the monitor

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C Output
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• To indicate a newline character, you can use the
  escape sequence \n
• Another way to advance output to a new line is to
  use the end line manipulator endl
• Inserting endl into the output stream causes a
  new line plus all waiting output to become
  visible, a process called flushing the buffer
• To create a program that declares two variables,
  assigns values to them, and creates output,
  perform the steps on pages 21 to 23 of the
  textbook

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Program Listing for Output1.cpp
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Output of Output1.cpp
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C Input
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• Many programs rely on input from a user
• These are called interactive programs because the
  user interacts with the program statements
• You create prompts by using the cout object you
  retrieve user responses by using the cin object
• The cin (pronounced see in) object fetches values
  from the keyboard
• It is used with the extraction operator gtgt
• Prior to a cin statement, it is almost always
  necessary to provide the user with a prompt, or a
  short explanation of what is expected

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C Input
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• Whitespace consists of any number of spaces,
  tabs, and Enter characters
• You will add prompts and interactive input to the
  Output1.cpp program by following the instructions
  shown on pages 24 and 25 of the textbook

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Output of Output2.cpp
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C Classes and Objects
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• When you use data types like int, char, and
  double within a program, you are using the C
  built-in, primitive or scalar data types
• A major feature of object-oriented languages is
  the ability to create your own new, complex data
  types
• These new types are called classes
• A class can contain many simpler data types
  within it, as well as any number of functions
• The relationship between these components, or
  fields, is often called a has-a relationship

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C Classes and Objects
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A Complete Class Definition and a main( ) Method
that Uses a Class Object
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C Classes and Objects
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• You will create a Student class, and then create
  a program that uses a Student class object using
  the procedures outlined on pages 27 and 28 of the
  textbook
• Creating a class provides a means to group data
  fields together in a logical way

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Summary
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• Programming a computer involves learning the
  syntax of a computer programming language and
  resolving logical errors
• All programming languages provide methods for
  input and output of variable values
• You declare a variable by providing it with a
  name and a type
• Procedural programs consist of a series of steps
  or procedures that take place one after the other
• Object-oriented programming adds several new
  programming concepts including objects, classes,
  inheritance, and polymorphism

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Summary
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• You write a C program by typing source code
  into an editor and compiling the program
• C modules are called functions, and each
  function contains a header and a body
• C variables must be given a type and a name
• Simple types include integer for whole numbers,
  double and float for floating-point values, and
  character for any character
• Comments are non-executing program statements

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Summary
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• C supports line comments and block comments
• A preprocessor directive tells the compiler to do
  something, such as to include a header file,
  before compiling the program
• The cout statement (along with an insertion
  operator) is used to display values
• When you create a class, you create your own C
  data type, which is a complex type composed of
  simpler types