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Note for Computer Network - CN by rajnish kumar

  • Computer Network - CN
  • Note
  • AKU PATNA - GCE
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Abstract Data Types Abstract Data type (ADT) is a type (or class) for objects whose behaviour is defined by a set of value and a set of operations. The definition of ADT only mentions what operations are to be performed but not how these operations will be implemented. It does not specify how data will be organized in memory and what algorithms will be used for implementing the operations. It is called “abstract” because it gives an implementation independent view. The process of providing only the essentials and hiding the details is known as abstraction. The user of data type need not know that data type is implemented, for example, we have been using int, float, char data types only with the knowledge with values that can take and operations that can be performed on them without any idea of how these types are implemented. So a user only needs to know what a data type can do but not how it will do it. We can think of ADT as a black box which hides the inner structure and design of the data type. Now we’ll define three ADTs namely List ADT, Stack ADT, Queue ADT. List ADT A list contains elements of same type arranged in sequential order and following operations can be performed on the list. get() – Return an element from the list at any given position. insert() – Insert an element at any position of the list. remove() – Remove the first occurrence of any element from a non-empty list. remove At() – Remove the element at a specified location from a non-empty list. replace() – Replace an element at any position by another element. size() – Return the number of elements in the list. is Empty() – Return true if the list is empty, otherwise return false. is Full() – Return true if the list is full, otherwise return false. Stack ADT A Stack contains elements of same type arranged in sequential order. All operations takes place at a single end that is top of the stack and following operations can be performed: push() – Insert an element at one end of the stack called top. pop() – Remove and return the element at the top of the stack, if it is not empty. peek() – Return the element at the top of the stack without removing it, if the stack is not empty. size() – Return the number of elements in the stack. is Empty() – Return true if the stack is empty, otherwise return false. is Full() – Return true if the stack is full, otherwise return false. Queue ADT A Queue contains elements of same type arranged in sequential order. Operations takes place at both ends, insertion is done at end and deletion is done at front. Following operations can be performed: enqueue() – Insert an element at the end of the queue. dequeue() – Remove and return the first element of queue, if the queue is not empty. peek() – Return the element of the queue without removing it, if the queue is not empty. size() – Return the number of elements in the queue.

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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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