Engineering Problem Solving With C An Object Based Approach

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Engineering Problem Solving With CAn Object
Based Approach

• Chapter 8
• Introduction to Classes

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Classes

• The building blocks of object oriented
  programming
• Include function members and data members
• A well designed class is as easy to use as a
  pre-defined data type

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Designing a Class

• Desired operations
• Member functions or methods
• constructors
• accessor functions
• overloaded operators
• (functions that do the work)
• Required data members

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Writing a Class Definition

• A class definition has two parts
• Class declaration
• defines name of class, data members, and
  prototypes for member functions
• Class implementation
• implements the member functions

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Class Declaration

• Name of the class is specified using the key word
  class
• Body of the class declaration includes
• declaration statements for the data members
• function prototypes
• Keywords public, private and protected specify
  the accessibility of the class members

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Example - Date Class Declaration

• include ltiostreamgt
• using namespace std
• class Date
• //class body
• public
• void input(istream) // I/O methods
• void print(ostream) const
• void setDate(int mo, int d, int y)
• int get_day() const // access methods
• int get_month() const
• int get_year() const
• private
• int day, month, year

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Date Class

• Name of the class is Date
• Three private data members
• Six public function members
• Data members can only be accessed by the member
  functions

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Class Implementation

• Includes
• Function definitions for all function members
• Scope Resolution Operator () specifies a
  function as a member of a class

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Implementation of Date Class

• include Date.h
• void Dateinput(istream in)
• in gtgt month gtgt day gtgt year
• void Dateprint(ostream out) const
• out ltlt month ltlt/ ltltday ltlt / ltlt year
• void Dateset_date(int m, int d, int y)
• month m
• day d
• year y

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Accessor Functions

• Required to access private data members
• Complete set should be provided
• Our Date class requires 3 accessor functions

int get_day() const int get_month() const int
get_year() const

• const should be placed at the end of any
  function that is not intended to modify the
  calling object.

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Initializing Objects

• Constructor functions are used to initialize
  objects at the time they are declared
• Called automatically
• Same name as the class name
• No return value, not even void

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Constructors for the Date Class

• Default Constructor
• constructor with no parameters
• Prototype
• Date()
• Constructor with Parameters
• Prototype
• Date(int m, int d, int y)

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Default Constructor

• Definition
• DateDate() month(1), day(1), year(2002)
• or
• DateDate()
• month 1
• day 1
• year 2000
• First definition is preferred.

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Constructors With Parameters

• Definition
• DateDate(int m, int d, int y)month(m), day(d),
  year(y)
• or
• DateDate(int m, int d, int y)
• month m
• day d
• year y

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Using Programmer Defined Classes

• Separate Compilation
• Class declaration is saved in a file named
  classname.h
• Class implementation is saved in a file named
  classname.cpp (or whatever extension your
  compiler expects)
• .h file is included in user program and
  implementation file
• User program is linked to implementation file

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Using the Date Class

• include Date.h
• int main()
• Date today(4,6,2002), birthday
• //member functions are called using the dot
  operator
• birthday.input(cin)
• today.print(cout)
• birthday.print(cout)
• if(today.get_day() birthday.get_day()
• today.get_month() birthday.get_month()
  )
• cout ltlt happy birthday!

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Practice!

• Given this definition of a class for a rational
  number implement the default constructor,
  parameterized constructor, and the input
  function.
• class rational
• private
• int num, denom
• public
• rational( ) // initialize to 1/1
• rational(int n, int d)
• void input (istream istr ) const
• void output (ostream ostr) // write as
  num/denom
• bool improper() const // true if num gt denom

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Answer to practice!
include "rational.h"
rationalrational( )num(1),denom(1)
rationalrational(int n, int d)num(n),denom(d)

void rationalinput (istream istr )
istr gtgt num gtgt denom
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Operators

• Assignment operator is defined for objects of the
  same type
• Date d1, d2
• d1.input(cin)
• d2 d1
• Other operators are not predefined, but can be
  overloaded in the class definition(see chapter
  10)
• arithmetic, relational, logical, input and output

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Helper Functions

• Member functions
• Called by other member functions
• Usually specified as private

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Example

• Design a class to implement a unit vector. A
  vector object will be represented by an anchor
  point (the base of the arrow), and an
  orientation(always between 0 and 360 degrees). 
  There are 2 manipulations that you can perform on
  a vector without changing its length.
• translate (slide) the vector in the plane,
  changing its position but not its orientation.
• rotate a vector, changing its orientation

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Translation - change position but not orientation
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Rotation - change orientation around anchor point
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Class Declaration
class UnitVector public
UnitVector() //
contstructors UnitVector(double init_x,
double init_y, double init_orientation)
void rotate(double d_orient)     //
rotate the vector void
translate(double dx, double dy) // translate
the // vector. private
//helper function     void
fix_orientation()   // Calculate a legal
orientation      double x,
y                   // The anchor point of the
object.      int orientation
//orientation
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Class Implementation
//Constructor functions UnitVectorUnitVector(dou
ble initial_x, double initial_y, double
initial_orientation) x(initial_x),
y(initial_y), orientation(initial_orientation
) fix_orientation() UnitVectorUnitVector(
) x(0), y(0), orientation 0
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Member Function Definitions
// rotate the calling vector void
UnitVectorrotate(double d_orient)       orient
ation d_orient fix_orientation() //
translate the calling vector void
UnitVectortranslate(double dx, double dy) x
dx y dy
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Helper Function Definition
//This function adjusts the orientation value
//Original orientation may be lt 0 or gt 360)
//Adjusted orientation is 0ltorientation lt 360.
void UnitVectorfix_orientation()  
if(orientation lt 0) orientation 360
orientation360 else orientation
orientation360
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Passing Objects To Functions

• Objects may be passed either "by value" or "by
  reference"
• Example

bool UnitVectorShareBasePoint(UnitVector
v)const ( if (x v.x y v.y) return
true else return false
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Practice!

• Which of the statements on the right is valid
  within a main program which contains an include
  for this header file.
• class rational
• private
• int num, denom
• int LCD( )
• public
• rational( )
• rational(int n, int d)
• void input (istream istr )
• void output (ostream ostr) const
• void reduce ( )

• rational A
• rational B(5, 9)
• input(A)
• B.output(cout)
• int divB.LCD()
• A.denom 3
• B.reduce

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