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Note for Computer Network - CN by rajnish kumar

  • Computer Network - CN
  • Note
  • AKU PATNA - GCE
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is Empty() – Return true if the queue is empty, otherwise return false. is Full() – Return true if the queue is full, otherwise return false. From these definitions, we can clearly see that the definitions do not specify how these ADTs will be represented and how the operations will be carried out. There can be different ways to implement an ADT, for example, the List ADT can be implemented using arrays, or singly linked list or doubly linked list. Similarly, stack ADT and Queue ADT can be implemented using arrays or linked lists. Inheritance The capability of a class to derive properties and characteristics from another class is called Inheritance. Inheritance is one of the most important feature of Object Oriented Programming. Sub Class: The class that inherits properties from another class is called Sub class or Derived Class. Super Class:The class whose properties are inherited by sub class is called Base Class or Super class. Why and when to use inheritance? Consider a group of vehicles. You need to create classes for Bus, Car and Truck. The methods fuelAmount(), capacity(), applyBrakes() will be same for all of the three classes. If we create these classes avoiding inheritance then we have to write all of these functions in each of the three classes as shown in below figure: You can clearly see that above process results in duplication of same code 3 times. This increases the chances of error and data redundancy. To avoid this type of situation, inheritance is used. If we create a class Vehicle and write these three functions in it and inherit the rest of the classes from the vehicle class, then we can simply avoid the duplication of data and increase re-usability. Look at the below diagram in which the three classes are inherited from vehicle class:

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Using inheritance, we have to write the functions only one time instead of three times as we have inherited rest of the three classes from base class(Vehicle). Implementing inheritance in C++: For creating a sub-class which is inherited from the base class we have to follow the below syntax. Syntax: class subclass_name : access_mode base_class_name { //body of subclass }; Here, subclass_name is the name of the sub class, access_mode is the mode in which you want to inherit this sub class for example: public, private etc. and base_class_name is the name of the base class from which you want to inherit the sub class. Note: A derived class doesn’t inherit access to private data members. However, it does inherit a full parent object, which contains any private members which that class declares. class Parent { public: int id_p; }; // Sub class inheriting from Base Class(Parent) class Child : public Parent { public: int id_c; }; //main function int main() { Child obj1;

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// An object of class child has all data members // and member functions of class parent obj1.id_c = 7; obj1.id_p = 91; cout << "Child id is " << obj1.id_c << endl; cout << "Parent id is " << obj1.id_p << endl; return 0; } Output: Child id is 7 Parent id is 91 In the above program the ‘Child’ class is publicly inherited from the ‘Parent’ class so the public data members of the class ‘Parent’ will also be inherited by the class ‘Child’. Modes of Inheritance 1. Public mode: If we derive a sub class from a public base class. Then the public member of the base class will become public in the derived class and protected members of the base class will become protected in derived class. 2. Protected mode: If we derive a sub class from a Protected base class. Then both public member and protected members of the base class will become protected in derived class. 3. Private mode: If we derive a sub class from a Private base class. Then both public member and protected members of the base class will become Private in derived class. Note : The private members in the base class cannot be directly accessed in the derived class, while protected members can be directly accessed. For example, Classes B, C and D all contain the variables x, y and z in below example. It is just question of access. filter_none brightness_4 // C++ Implementation to show that a derived class // doesn’t inherit access to private data members. // However, it does inherit a full parent object class A { public: int x; protected: int y; private: int z; }; class B { // // // }; : public A x is public y is protected z is not accessible from B

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class C { // // // }; class D { // // // }; : protected A x is protected y is protected z is not accessible from C : private A // 'private' is default for classes x is private y is private z is not accessible from D The below table summarizes the above three modes and shows the access specifier of the members of base class in the sub class when derived in public, protected and private modes: Types of Inheritance in C++ 1. Single Inheritance: In single inheritance, a class is allowed to inherit from only one class. i.e. one sub class is inherited by one base class only. Syntax: 2. class subclass_name : access_mode base_class 3. { 4. //body of subclass 5. }; filter_none

Lecture Notes