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Abstract Data Type

Abstract Data Type. Data Structures. Main Notions and Definitions. Atomic Data. Data Structure. A Data Structure is an aggregation of atomic and composite data into a set with defined relationships. Structure means a set of rules that holds the data together.

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Abstract Data Type

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  1. Abstract Data Type Data Structures. Main Notions and Definitions.

  2. Atomic Data

  3. Data Structure • A Data Structure is an aggregation of atomic and composite data into a set with defined relationships. • Structure means a set of rules that holds the data together. • Taking a combination of data and fit them into such a structure that we can define its relating rules, we create a data structure.

  4. Composite Data Structures

  5. Data Structure is: • A combination of elements in which each is either a data type or another data structure • A set of associations or relationships involving the combined elements

  6. Data Structures: Properties • Most of the modern programming languages support a number of data structures. • In addition, modern programming languages allow programmers to create new data structures for an application. • Data structures can be nested. A data structure may contain other data structures (array of arrays, array of records, record of records, record of arrays, etc.)

  7. Some Data Structures

  8. Pseudocode • Pseudocode is a pseudo programming language, which is commonly used to define algorithms • Pseudocode is a natural language-like representation of the algorithm logic • Its structure is close to the structure of the most high level programming languages, but it is free from many unnecessary details

  9. Data Structures: A Pseudocode Approach with C

  10. Data Structures: A Pseudocode Approach with C

  11. The Abstract Data Type (ADT) • We know what a data type can do • How it is done is hidden for the user The concept of abstraction means: • With an ADT users are not concerned with how the task is done but rather with what it can do.

  12. ADT: Example • The program code to read/write some data is ADT. It has a data structure (character, array of characters, array of integers, array of floating-point numbers, etc.) and a set of operations that can be used to read/write that data structure.

  13. The Abstract Data Type (ADT) • A data declaration packaged together with the operations that are meaningful for the data type. • In other words, we encapsulate the data and the operations on the data, and then we hide them from the user. The Abstract Data Type (ADT) is: • Declaration of data • Declaration of operations • Encapsulation of data and operations

  14. The Abstract Data Type (ADT) • All references to and manipulation of the data in a structure must be handled through defined interfaces to the structure. • Allowing the application program to directly reference the data structure is a common fault in many implementations. • It is necessary for multiply versions of the structure to be able to coexist. • We must hide the implementation from the user while being able to store different data.

  15. ADT Operations • Data are entered, accessed, modified and deleted through the external interface, which is a “passageway” located partially “in” and partially out of the ADT. • Only the public functions are accessible through this interface. • For each ADT operation there is an algorithm that performs its specific task.

  16. Typical ADTs: • Lists • Stacks • Queues • Trees • Heaps • Graphs

  17. 1-4 ADT Implementations There are two basic structures we can use to implement an ADT list: arrays and linked lists. In this section we discuss the basic linked-list implementation.

  18. Array Implementations • In an array, the sequentiality of a list is maintained by the order structure of elements in the array (indexes). • Although searching an array for an individual element can be very efficient, insertion and deletion of elements are complex and inefficient processes.

  19. Linked Lists • A Linked List is an ordered collection of data in which each element contains the location of the next element or elements. • In a linked list, each element contains two parts: data and one or more links. • The data part holds the application data – the data to be processed. • Links are used to chain the data together. They contain pointers that identify the next element or elements in the list.

  20. Linear and non-linear Linked Lists • In linear linked lists, each element has only zero or one successor. • In non-linear linked lists, each element can have zero, one or more successors.

  21. Nodes • A node is a structure that has two parts: the data and one or more links. • The nodes in a linked list are called self-referential structures. In such a structure, each instance of the structure contains one or more pointers to other instances of the same structural type.

  22. Nodes • The data part in a node can be a single field, multiple fields, or a structure that contains several fields, but it always acts as a single field.

  23. Linked Lists vs. Arrays • The major advantage of the linked list over the array is that data are easily inserted and deleted. • It is not necessary to shift elements of a linked list to make room for a new elements or to delete an element. • However, because the elements are no longer physically sequenced in a linked list, we are limited to sequential searches.

  24. 1-5 Generic Code for ADT In this section we discuss and provide examples of two tools that are required to implement an ADT. • Pointer to Void • Pointer to Function

  25. Generic Code • In data structures we need to create generic code for abstract data types. • Generic code allows us to write one set of code and apply it to any data type. • For example, we can write generic functions to implement a stack structure. We can then use the generic functions to implement an integer stack, a float stack, etc.

  26. Data Pointer • A pointer is a programming language data type whose value refers directly to ("points to") another value stored elsewhere in the computer memory using its address. Obtaining the value that a pointer refers to is called dereferencing the pointer.

  27. Pointer to void • Casting of the pointer is its connection with particular data type. • Major programming languages are strongly typed. This means that operations such as assign and compare must use compatible types or be cast to compatible types. • The only exception is the pointer to void, which can be assigned without a cast. • This means that a pointer to void is a generic pointer that can be used to represent any data type.

  28. Pointer to void

  29. Pointer to void

  30. Pointer to void • Important remark: a pointer to void cannot be dereferencedunless it is cast. • In other words, we cannot use *p without casting (without connection of the pointer with particular data type).

  31. Functionmalloc • This function in C (a similar function is presented in all modern programming languages) returns a pointer to void. • This function is used to dynamically allocate any type of data. • This is a generic function that returns a pointer to void (void*). It can be used for returning a pointer to any data type. For example, a pointer to an integer can be created using intPtr = (int*)malloc (sizeof (int))

  32. Pointer to Node

  33. (Continued)

  34. Homework • Sections 1.1-1.5

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