11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 1 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 M ethods 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 2

PROGRAMMER DEFINED TYPES 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 3

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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 4

Programmer Defined Types The DOG directory has an example of a class to represent a dog. dogProg.cpp Has: Class declaration, class implementation and a testing main() – For simplicity all three parts are in one file 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 5

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 6 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.

Point Class  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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 7

Point Class – Special Methods  xCoord and yCoord are private. – main() and other outside functions cannot see them.  Accessor methods allow other functions to see them. – getX(), getY()  Mutator methods all outside functions to change the attributes. – setX(), setY() 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 8

UML CLASS DIAGRAM FOR POINT 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 9 Point -xCoord -yCoord getX() +getY() +setX() +setY() +operator –() Note: - => private + => public

DESIGN AND IMPLEMENTATION OF CLASSES class declaration class implementation 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 10

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 11 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

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 12 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.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 13 Example - Point class Declaration //Point class declaration: // filename: Point.h class Point { private: double xCoord, yCoord;//private attributes public: //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!

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 14 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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 15 Syntax: return type class-name::method-name([parameter list])[modifier]

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 16 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).

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 17 Implementation of Point class //implementation for Point //filename: Point.cpp #include "Point.h" //Required for Point #include //Required for sqrt(),pow() //accessor method double Point::getX() const { return xCoord; } //mutator method void 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; } 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 18 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 //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; } 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 19 Output: 5.1

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber Sphere class Design and implement a class called Sphere that contains member data that represents the sphere’s diameter. Give the class accessor and mutator functions. Include functions to find the volume and the surface area of the Sphere. Write a main function to create and test a Sphere.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber Start Here, 4/25/12 Quiz 8, Friday, 04/27/12 On 8.1 and 8.2 See question in Practice! On page 353.

CONSTRUCTORS default constructors parameterized constructors function overloading 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 22

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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 23 Syntax: class-name::class-name([parameter list])[:initialization list] { }

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 24 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.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 25 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.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 26 Default Constructor: Point  Definition: add to Point.cpp Point::Point() { xCoord = yCoord = 0; } or

Example: Default Constructor Point p1; //Default constructor is called. Memory snapshot: Point p1 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber double xCoord double yCoord

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 28 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 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber double xCoord double yCoord

Point.h Revisited: 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 30 //Point class declaration: // filename: Point.h class Point { private: double xCoord, yCoord;//private attributes public: //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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 31

Function Overloading  Example in ch8/ovldmean.cpp 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 32

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 33 Practice! Add two constructors to this Rational class class Rational {private: int num, denom; public: rational( );// initialize to 1/1 rational(int n, int d); int getNum(); int getDenom(); };

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 34 Practice! Implement the following class declaration, Also include the constructors from the previous slide: class Rational {private: int num, denom; public: Rational( );// initialize to 1/1 Rational(int n, int d); int getNum(); int getDenom(); };

CLASS COMPOSITION 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 35

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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 36

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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 37

UML CLASS COMPOSITION DIAGRAM 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 38 Rectangle Point 1 -double width -double height -Point origin

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber Rectangle Composition Class Code is in ch8/EtterRectangle Must compile the Point class along with the Rectangle class so the Rectangle can use that class testRectangle.cpp tests the class.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber Rectangle Composition Class Code is in ch8/EtterRectangle Let’s test the setOrigin() function

THE VECTOR CLASS parameter passing 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 41

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. 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 42

11/07/11J. Ingber Introduction to C++43 vector Objects  We can define an instance of the vector class in a type declaration statement. Syntax: vector identifier[(size,initial-value)] Examples: vector list; //empty vector vector wordList(n); //capacity:n strings //vector of 8 integers, each initialized to 0 vector intList(8,0);

11/07/11J. Ingber Introduction to C++44 vector class  #include //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

11/07/11J. Ingber Introduction to C++45 Operators  The square bracket operator ( [ ] ) is defined for vector objects.  The assignment operator ( = )is defined for vectors of the same type. Example: vector list(10); vector 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 & dVec, double sFactor); void print(vector dVec);//pass by value void print2(const vector & dVec); Point closeToOrigin(vector pointVec); 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 46

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber Programming Example Vector.cpp Inputs a list of ints Outputs the numbers in the order entered and in reverse order Don’t have to the number of integers before execution.

PRIVATE METHODS 11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 48

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 49 Helper Methods  private or protected member functions.  Called by other member functions.  Designed to "help" behind the scenes.

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 50 Example Design a class to implement the mathematical concept of a unit vector. Attributes: an anchor point (the base of the vector) an orientation of degrees. Methods: translate(double dx, double dy): rotate (int dDegrees);

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 51 Translation - change position but not orientation

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 52 Rotation - change orientation around anchor point

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 53 Class Declaration class 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 };

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 54 Class Implementation //Constructors UnitVector::UnitVector(double initX, double initY, int initO)) : x(initX), y(initY), orientation(initO) { fixOrientation(); } UnitVector::UnitVector( ): x(0), y(0), orientation(0) { }

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 55 Member Function Definitions // rotate the calling vector void UnitVector::rotate(int d_orient) {orientation += d_orient; fixOrientation(); } // translate the calling vector void UnitVector::translate(double dx, double dy) {x += dx; y += dy; }

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 56 Helper Function Definition //This function adjusts the orientation value //Original orientation may be = 360) //Adjusted orientation is 0<=orientation < 360. void UnitVector::fixOrientation() { if(orientation < 0) orientation = orientation%360; else orientation = orientation%360; }

11/07/11Engineering Problem Solving with C++, second edition, J. Ingber 57 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();