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Engineering Problem Solving with C++, Etter/Ingber. Chapter 8 An Introduction to Classes 04-18-12. 11/07/11. Engineering Problem Solving with C++, second edition, J. Ingber. 1. An Introduction To Classes. Programmer Defined Types Design and Implementation of Classes Constructors.

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11/07/11

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  1. Engineering Problem Solving with C++, Etter/Ingber Chapter 8 An Introduction to Classes 04-18-12 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 1

  2. An Introduction To Classes • Programmer Defined Types • Design and Implementation of Classes • Constructors 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 2

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

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

  5. The Dog Class • 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 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 5

  6. Class • Class Declaration • Starts with keyword class • Name should begin with uppercase • Prototypes for member functions • Data members to store data for an object. • Class Implementation • Define class member functions. • Create objects main() testing function • Dog fifi; 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 6

  7. 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. Data members are private. • A good public interface and encapsulation allow for efficient maintenance and expandability of the class type. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 7

  8. 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 8

  9. 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() 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 9

  10. UML CLASS DIAGRAM FOR POINT Point -xCoord -yCoord getX() +getY() +setX() +setY() +operator –() Note: - => private + => public 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 10

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

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

  13. 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 controlthe accessibility of the attributes and methods. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 13

  14. 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! 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 14

  15. 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 15

  16. 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. Syntax: return type class-name::method-name([parameter list])[modifier] 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 16

  17. 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). 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 17

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

  19. 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; } xCoord and yCoord are provided by the calling object. std:: is required when the using namespace std; statement is not given. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 19

  20. 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; } Output: 5.1 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 20

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

  22. Engineering 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.

  23. default constructors parameterized constructors function overloading CONSTRUCTORS 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 23

  24. 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. Syntax: class-name::class-name([parameter list])[:initialization list] { } 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 24

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

  26. 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 26

  27. Default Constructor: Point • Definition: add to Point.cpp Point::Point() { xCoord = yCoord = 0; } or 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 27

  28. Example: Default Constructor Point p1; //Default constructor is called. Memory snapshot: Point p1 0.0 double xCoord 0.0 double yCoord 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 28

  29. 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; } 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 29

  30. Example: Parameterized Constructor Point p1(1.5, 4.2); //Parameterized constructor. Memory snapshot: Point p1 double xCoord 1.5 4.2 double yCoord 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 30

  31. Point.h Revisited: //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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 31

  32. 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 32

  33. Function Overloading • Example in ch8/ovldmean.cpp 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 33

  34. 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(); }; 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 34

  35. 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(); }; 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 35

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

  37. Class Composition • Object oriented problem solutions are built around class hierarchies and associations. • Classcomposition 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 37

  38. 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 38

  39. UML CLASS COMPOSITION DIAGRAM Rectangle • double width • double height • Point origin 1 Point 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 39

  40. Engineering 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.

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

  42. parameter passing THE VECTOR CLASS 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 42

  43. The vector class • The vector class is a pre-defined classtemplate 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. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 43

  44. vector Objects • We can define an instance of the vectorclass in a type declaration statement. Syntax: vector<data-type> identifier[(size,initial-value)] Examples: vector <double> list; //empty vector vector<string> wordList(n); //capacity:n strings //vector of 8 integers, each initialized to 0 vector<int> intList(8,0); 11/07/11 J. Ingber Introduction to C++ 44

  45. 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 11/07/11 J. Ingber Introduction to C++ 45

  46. 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 11/07/11 J. Ingber Introduction to C++ 46

  47. 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); 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 47

  48. Engineering 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.

  49. PRIVATE METHODS 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 49

  50. Helper Methods • private or protected member functions. • Called by other member functions. • Designed to "help" behind the scenes. 11/07/11 Engineering Problem Solving with C++, second edition, J. Ingber 50

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