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OOPs & C++ UNIT 3

The document provides information about object-oriented programming concepts in C++ including class, object, constructor, destructor, access specifiers, data members, member functions, static members, and friend functions. It defines each concept, provides syntax examples, and explains how to create a class, make objects, and access members. Constructors are used to initialize objects while destructors deallocate memory. Access specifiers determine public, private, and protected access.

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OOPs & C++ UNIT 3 BY:SURBHI SAROHA
SYLLABUS  Class  Object  Constructor & Destructor  Class Modifiers(Private, Public & Protected)  Data Member  Member Function  Static Data Member  Static Member Function  Friend Function
Cont….  Object  Constructor(Default Constructor , Parameterized Constructor and Copy Constructor)  Destructor
Class  C++ is an object-oriented programming language.  Everything in C++ is associated with classes and objects, along with its attributes and methods.  For example: in real life, a car is an object.  The car has attributes, such as weight and color, and methods, such as drive and brake.  Attributes and methods are basically variables and functions that belongs to the class.  These are often referred to as "class members".  A class is a user-defined data type that we can use in our program, and it works as an object constructor, or a "blueprint" for creating objects.
Create a Class  To create a class, use the class keyword:  Example  Create a class called "MyClass":  class MyClass { // The class  public: // Access specifier  int myNum; // Attribute (int variable)  string myString; // Attribute (string variable)  };
Create an Object  In C++, an object is created from a class. We have already created the class named MyClass, so now we can use this to create objects.  To create an object of MyClass, specify the class name, followed by the object name.  To access the class attributes (myNum and myString), use the dot syntax (.) on the object:  Example  Create an object called "myObj" and access the attributes:  class MyClass { // The class  public: // Access specifier
Cont….  int myNum; // Attribute (int variable)  string myString; // Attribute (string variable)  };  int main() {  MyClass myObj; // Create an object of MyClass  // Access attributes and set values 
Cont….  myObj.myNum = 15;  myObj.myString = "Some text";  // Print attribute values  cout << myObj.myNum << "n";  cout << myObj.myString;  return 0;  }
Constructor & Destructor  A constructor is a member function of a class that has the same name as the class name.  It helps to initialize the object of a class.  It can either accept the arguments or not.  It is used to allocate the memory to an object of the class.  It is called whenever an instance of the class is created.  It can be defined manually with arguments or without arguments.  There can be many constructors in a class.  It can be overloaded but it can not be inherited or virtual.  There is a concept of copy constructor which is used to initialize an object from another object.
Syntax:  ClassName()  {  //Constructor's Body  }
Destructor  Like a constructor, Destructor is also a member function of a class that has the same name as the class name preceded by a tilde(~) operator.  It helps to deallocate the memory of an object.  It is called while the object of the class is freed or deleted.  In a class, there is always a single destructor without any parameters so it can’t be overloaded.  It is always called in the reverse order of the constructor.  if a class is inherited by another class and both the classes have a destructor then the destructor of the child class is called first, followed by the destructor of the parent or base class.
Destructor  ~ClassName()  {  //Destructor's Body  }
Class Modifiers(Private, Public & Protected)  In C++, there are three access specifiers:  public - members are accessible from outside the class  private - members cannot be accessed (or viewed) from outside the class  protected - members cannot be accessed from outside the class, however, they can be accessed in inherited classes.
Example  #include <iostream>  using namespace std;  class MyClass {  public: // Public access specifier  int x; // Public attribute  private: // Private access specifier  int y; // Private attribute  };
Cont….  int main() {  MyClass myObj;  myObj.x = 25; // Allowed (x is public)  myObj.y = 50; // Not allowed (y is private)  return 0;  }
Data Member  Data members include members that are declared with any of the fundamental types, as well as other types, including pointer, reference, array types, bit fields, and user-defined types.  You can declare a data member the same way as a variable, except that explicit initializers are not allowed inside the class definition.  However, a const static data member of integral or enumeration type may have an explicit initializer.  If an array is declared as a nonstatic class member, you must specify all of the dimensions of the array.  A class can have members that are of a class type or are pointers or references to a class type. Members that are of a class type must be of a class type that has been previously declared. An incomplete class type can be used in a member declaration as long as the size of the class is not needed. For example, a member can be declared that is a pointer to an incomplete class type.
Member Function  Member functions are operators and functions that are declared as members of a class.  Member functions do not include operators and functions declared with the friend specifier.  These are called friends of a class.  You can declare a member function as static; this is called a static member function.  A member function that is not declared as static is called a nonstatic member function.  class x { public: int add() // inline member function  add {return a+b+c;};  private: int a,b,c;  };
Static Data Member  Static data members are class members that are declared using static keywords. A static member has certain special characteristics which are as follows:  Only one copy of that member is created for the entire class and is shared by all the objects of that class, no matter how many objects are created.  It is initialized before any object of this class is created, even before the main starts.  It is visible only within the class, but its lifetime is the entire program.  Syntax:  static data_type data_member_name;
// C++ Program to demonstrate // the working of static data member  #include <iostream>  using namespace std;  class A {  public:  A()  {  cout << "A's Constructor Called " <<  endl;  }  }; 
Cont….  class B {  static A a;   public:  B()  {  cout << "B's Constructor Called " <<  endl;  }  }; 
Cont….  // Driver code  int main()  {  B b;  return 0;  }
Static Member Function  Static Member Function in a class is the function that is declared as static because of which function attains certain properties as defined below:  A static member function is independent of any object of the class.  A static member function can be called even if no objects of the class exist.  A static member function can also be accessed using the class name through the scope resolution operator.  A static member function can access static data members and static member functions inside or outside of the class.  Static member functions have a scope inside the class and cannot access the current object pointer.  You can also use a static member function to determine how many objects of the class have been created.
// C++ Program to show the working of // static member functions  #include <iostream>  using namespace std;   class Box  {  private:  static int length;  static int breadth;  static int height;   public: 
Cont….  static void print()  {  cout << "The value of the length is: " << length << endl;  cout << "The value of the breadth is: " << breadth << endl;  cout << "The value of the height is: " << height << endl;  }  };
Cont….  // initialize the static data members  int Box :: length = 10;  int Box :: breadth = 20;  int Box :: height = 30;   // Driver Code   int main()  {   Box b; 
Cont….  cout << "Static member function is called through Object name: n" << endl;  b.print();   cout << "nStatic member function is called through Class name: n" << endl;  Box::print();   return 0;  }
Output  Static member function is called through Object name:  The value of the length is: 10  The value of the breadth is: 20  The value of the height is: 30  Static member function is called through Class name:  The value of the length is: 10  The value of the breadth is: 20  The value of the height is: 30
Friend Function  A friend class can access private and protected members of other classes in which it is declared as a friend.  It is sometimes useful to allow a particular class to access private and protected members of other classes.  For example, a LinkedList class may be allowed to access private members of Node.  We can declare a friend class in C++ by using the friend keyword.  Syntax:  friend class class_name; // declared in the base class
Cont…..  If a function is defined as a friend function in C++, then the protected and private data of a class can be accessed using the function.  By using the keyword friend compiler knows the given function is a friend function.  For accessing the data, the declaration of a friend function should be done inside the body of a class starting with the keyword friend.
Advantages of Friend Function in C++  The friend function allows the programmer to generate more efficient codes.  It allows the sharing of private class information by a non-member function.  It accesses the non-public members of a class easily.  It is widely used in cases when two or more classes contain the interrelated members relative to other parts of the program.  It allows additional functionality that is not used by the class commonly.
Example  #include <iostream>  using namespace std;  class Distance {  private:  int meter;  // friend function  friend int addFive(Distance);  public:
Cont….  Distance() : meter(0) {}  };  // friend function definition  int addFive(Distance d) {  //accessing private members from the friend function  d.meter += 5;  return d.meter;  }  int main() {
Cont….  Distance D;  cout << "Distance: " << addFive(D);  return 0;  }
Object  In C++, Object is a real world entity, for example, chair, car, pen, mobile, laptop etc.  In other words, object is an entity that has state and behavior.  Here, state means data and behavior means functionality.  Object is a runtime entity, it is created at runtime.
Constructor(Default Constructor , Parameterized Constructor and Copy Constructor)  A constructor in C++ is a special member function with exact same name as the class name.  The constructor name is the same as the Class Name. Reason: Compiler uses this character to differentiate constructors from the other member functions of the class.  A constructor must not declare a return type or void. Reason: As it’s automatically called and generally used for initializing values.  They can be defined inside or outside the class definition.  Automatically calls when an object is created for the class.  It uses to construct that means to initialize all the data members (variables) of the class.
Constructors types in C++  1. Default Constructor  A constructor with no arguments (or parameters) in the definition is a default constructor.  It is the type of constructor in C++ usually used to initialize data members (variables) with real values.  Note: The compiler automatically creates a default constructor without data member (variables) or initialization if no constructor is explicitly declared.
Default Constructor  #include <iostream>  using namespace std;   //Class Name: Default_construct  class Default_construct  {  public:  int a, b;   // Default Constructor  Default_construct()  { 
Cont….  a = 100;  b = 200;  }  };   int main()  {  Default_construct con; //Object created  cout << "Value of a: " << con.a;  cout<< "Value of b: " << con.b;  return 0;  }
2. Parameterized Constructor  Unlike the Default constructor, It contains parameters (or arguments) in the constructor definition and declaration.  More than one argument can also pass through a parameterized constructor.  #include <iostream>  using namespace std;   // class name: Rectangle  class Rectangle {  private:  double length;  double breadth;   public:
Cont….  // parameterized constructor  Rectangle(double l, double b) {  length = l;  breadth = b;  }   double calculateArea() {  return length * breadth;  }  };   int main() {  // create objects to call constructors
Cont….  Rectangle obj1(10,6);  Rectangle obj2(13,8);   cout << "Area of Rectangle 1: " << obj1.calculateArea();  cout << "Area of Rectangle 2: " << obj2.calculateArea();   return 0;  }
3. Copy Constructor  A copy constructor is the third type among various types of constructors in C++.  The member function initializes an object using another object of the same class.  It helps to copy data from one object to another.
Example  #include <iostream>  using namespace std;  // class name: Rectangle  class Rectangle {  private:  double length;  double breadth;  public:  // parameterized constructor  Rectangle(double l, double b) {  length = l;  breadth = b;  }
Cont….  // copy constructor with a Rectangle object as parameter copies data of the obj parameter  Rectangle(Rectangle &obj) {  length = obj.length;  breadth = obj.breadth;  }    double calculateArea() {  return length * breadth;  }  }; 
Cont….  int main() {  // create objects to call constructors  Rectangle obj1(10,6);  Rectangle obj2 = obj1; //copy the content using object   //print areas of rectangles  cout << "Area of Rectangle 1: " << obj1.calculateArea();  cout << "Area of Rectangle 2: " << obj2.calculateArea();   return 0;  }
Destructor  #include <iostream>  using namespace std;  class Employee  {  public:  Employee()  {  cout<<"Constructor Invoked"<<endl;  } 
Cont…..  ~Employee()  {  cout<<"Destructor Invoked"<<endl;  }  };  int main(void)  {  Employee e1; //creating an object of Employee  Employee e2; //creating an object of Employee  return 0;  }
Thank you 