Engineering Problem Solving with C++, Etter/Ingber

04/21/23 Engineering Problem Solving with C++, second edition, J. Ingber

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Engineering Problem Solving with C++, Etter/Ingber

Chapter 8

An Introduction to Classes

An Introduction To Classes

Programmer Defined Types Design and Implementation of Classes Class Composition Constructors The vector class private Methods


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PROGRAMMER DEFINED TYPES


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Data Types

A data type is a concrete implementation of a concept.

Built in types include:– int, double, char

Pre-defined class types include:– string, istream, ostream

Real world applications work with concepts that are not available as built-in or pre-defined types.


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Programmer Defined Types Consider the concept of a point in a plane, defined as a:

– xCoordinate

– yCoordinate

Subtraction between points can be defined as a binary operation that returns the distance between two points in a plane.Point p1, p2;

double dist;

dist = p2-p1;

As a programmer, we can define a new type named Point by defining a C++ class named Point.


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Programmer Defined Types

A well-designed class type provides:– a good public interface.

– encapsulation of the implementation.

A good public interface provides a complete yet minimal set of public operations.

Encapsulation hides the implementation from the user.

A good public interface and encapsulation allow for efficient maintenance and expandability of the class type.

DESIGN AND IMPLEMENTATION OF CLASSES

class declaration

class implementation


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Defining C++ Classes

The definition of a class consists of two parts:– The class declaration

• saved in a file with a .h extension

– The class implementation• saved in a file with a .cpp extension

• the .cpp file should #include the .h file


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The class Declaration

A class declaration begins with the key word class followed by an identifier that specifies the name of the new class.

The body of the class declaration is a statement block that includes:– declaration statements for the data members (attributes)

– prototypes for the member functions (methods)

Keywords public, protected and private control the accessibility of the attributes and methods.


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Example - Point class Declaration//Point class declaration:// filename: Point.hclass Point{

private: double xCoord, yCoord;//private attributespublic:

//Two accessor methods: double getX() const; double getY() const; //Two mutator methods: void setX(double newX); void setY(double newY); //Distance Formula double operator –(const Point& p2) const;}; semicolon is required!


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The Point class Declaration

Two private attributes (encapsulation). Five public methods (public interface). The use of the const modifier in the prototypes

of the accessor methods prohibits modification of the calling object.

The const modifier is not used with the mutator methods because the intent of a mutator method is modification of the calling object.

Method Definition A method is a function that is a member of class.

A method header must include the name of a class, followed by the scope resolution operator (::) and the name of the method.


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Syntax:return type class-name::method-name([parameter list])[modifier]


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The class Implementation

The class implementation includes a definition for each of the methods declared in the class declaration.

The scope resolution operator (::) is required in the method header to associate the method name with the name of the class in which the method is declared to be a member.

The class implementation file must include the class declaration (.h file).


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Implementation of Point class//implementation for Point//filename: Point.cpp

#include "Point.h" //Required for Point#include <cmath> //Required for sqrt(),pow()

//accessor methoddouble Point::getX() const{ return xCoord;}

//mutator methodvoid Point::setX(double newX){ xCoord = newX;}

Implementation of Point class

//Distance Formula

double Point::operator –(const Point& rhs) const

{

double t1, t2, d;

t1 = rhs.xCoord – xCoord; //(x2-x1)

t2 = rhs.yCoord – yCoord; //(y2-y1)

d = std::sqrt( std::pow(t1,2) + std::pow(t2,2) );

return d;

}


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std:: is required when the using namespace std; statement is not

given.

xCoord and yCoord are provided by the calling object.

The Calling Object An object is an instance of a class. Objects reference (call) the public methods defined for

their class.

Example:#include "Point.h" //Required for Point

#include <iostream> //Required for cout

int main()

{

//A Point has an xCoord and a yCoord

Point p1; //p1 is a Point

p1.setX(5.1); //p1 is the calling object

std::cout << p1.getX() << std::endl;

return 0;

}04/21/23 Engineering Problem Solving with

C++, second edition, J. Ingber16

Output:5.1

UML CLASS DIAGRAM FOR POINT


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Point

-xCoord-yCoord

+getX()+getY()+setX()+setY()

+operator –()

Note: - => private+ => public

CLASS COMPOSITION


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Class Composition Object oriented problem solutions are built around class hierarchies and associations.

Class composition is an association used to model a "has-a" relationship between classes:– the whole "has-a" component.

– the component is "part-of" the whole.

Class composition allows for efficient building of complex programmer defined types.


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Example:

A rectangle is a shape that has a:– point of origin– width– height

Implement the concept of a rectangle by defining a programmer defined type named Rectangle.


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UML CLASS COMPOSITION DIAGRAM


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Rectangle

Point

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-double width-double height-Point origin

CONSTRUCTORS

default constructors

parameterized constructors

function overloading


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Constructors

A constructor is a method designed to build an instance of a class.

A constructor has the same name as its class. A constructor has no specified return value. A constructor is called automatically each time an

object is defined.


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Syntax:class-name::class-name([parameter list])[:initialization list]{ }


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Constructors

There are two forms of constructors:– Default Constructor

• constructor with no formal parameters, other than default parameters.

• attributes are initialized to the default value.– Parameterized Constructor

• constructor with one or more formal parameters.• constructor arguments determine the initial

values of the attributes.


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Default Constructor: Point

Prototype: add to Point.h

Point();

or

Point(double x=0, double y=0);

x=0 and y=0 are default parameters.


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Default Constructor: Point Definition: add to Point.cpp

Point::Point(){ xCoord = yCoord = 0;}

or

Point::Point(double x, double y){ xCoord = x; yCoord = y;}

Example: Default Constructor

Point p1; //Default constructor is called.

Memory snapshot:

Point p1


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0.0

0.0

double xCoord

double yCoord


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Parameterized Constructor: Point

Prototype: add to Point.h

Point(double xVal, double yVal); Definition: add to Point.cpp

Point::Point(double xVal, double yVal){ xCoord = xVal; yCoord = yVal;}

Example: Parameterized Constructor

Point p1(1.5, 4.2); //Parameterized constructor.

Memory snapshot:

Point p1


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1.5

4.2

double xCoord

double yCoord

Point.h Revisited:


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//Point class declaration:// filename: Point.hclass Point{

private: double xCoord, yCoord;//private attributespublic:

//Two constructors: Point(); Point(double x, double y); //Two accessor methods: double getX() const; double getY() const; //Two mutator methods: void setX(double newX); void setY(double newY); //Distance Formula double operator –(const Point& p2) const;};

Point constructors are example of overloaded methods.

Function Overloading Function overloading occurs when one or more

functions have the same name.– Point();– Point(double x, double y);

Overloaded functions share the same name, but each function must have a unique function signature.

A function signature includes the :– function name

– parameter list

– modifiers

– return value is NOT part of the function signature.04/21/23 Engineering Problem Solving with

C++, second edition, J. Ingber31


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Practice!

Implement the following class declaration:

class Rational{ private:

int num, denom;public: rational( ); // initialize to 1/1

rational(int n, int d);int getNum();

int getDenom();};

THE VECTOR CLASSparameter passing


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The vector class The vector class is a pre-defined class template included in the C++ Standard Template Library.

The vector class provides a generic implementation of the concept of an array.

vector objects can increase and decrease their size dynamically.


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04/21/23 J. Ingber Introduction to C++ 35

vector Objects We can define an instance of the vector class

in a type declaration statement. Syntax:vector<data-type> identifier[(size,initial-value)]

Examples:vector <double> list; //empty vectorvector<string> wordList(n); //capacity:n strings

//vector of 8 integers, each initialized to 0vector<int> intList(8,0);


vector class

#include <vector> //pre-defined in STL Common member functions:

empty() // returns true if vector contains no values

pop_back() // deletes last element in vector

push_back() // add element to end of vector

resize() // changes the size of vector

size() // returns the size of vector

capacity() // returns the capacity of vector


Operators

The square bracket operator ( [ ] ) is defined for vector objects.

The assignment operator ( = )is defined for vectors of the same type.

Example:vector<int> list(10);vector<int>newList;list[0]=10;…newList = list;cout << newList.size() << endl; //method

Parameter Passing

When a vector object is passed as an argument to a function, the default is pass by value.

Pass by reference can be specified with the & operator.

Example:void scale(vector<double>& dVec, double sFactor);

void print(vector<double> dVec);//pass by value

void print2(const vector<double>& dVec);

Point closeToOrigin(vector<Point> pointVec);


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PRIVATE METHODS


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Helper Methods

private or protected member functions. Called by other member functions. Designed to "help" behind the scenes.


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Example

Design a class to implement the concept of a unit vector. Attributes:

an anchor point (the base of the vector) an orientation of 0 - 360 degrees.

Methods:translate(double dx, double dy):rotate (int dDegrees);


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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 Declarationclass UnitVector { public: UnitVector(); // contstructors UnitVector(double init_x, double init_y, int

init_orientation); void rotate(int d_orient); // rotate the vector void translate(double dx, double dy); // translate the

// vector. private: //helper function void fixOrientation(); // Calculate a legal orientation double x, y; // The anchor point of the object.

int orientation; //orientation};


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Class Implementation

//ConstructorsUnitVector::UnitVector(double initX, double initY, int initO)) : x(initX), y(initY), orientation(initO){

fixOrientation();}UnitVector::UnitVector( ): x(0), y(0), orientation(0){ }


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Member Function Definitions

// rotate the calling vectorvoid UnitVector::rotate(int d_orient) { orientation += d_orient;

fixOrientation();}// translate the calling vector void UnitVector::translate(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 < 0 or >= 360) //Adjusted orientation is 0<=orientation < 360. void UnitVector::fixOrientation() {

if(orientation < 0) orientation = 360 + orientation%360;

elseorientation = orientation%360;

}


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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);void reduce ( );

};

rational A;rational B(5, 9);input(A);B.output(cout);int div=B.LCD();A.denom = 3;B.reduce;

Engineering Problem Solving with C++, Etter/Ingber

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