CS341 PASCAL II - Data Structures1 PASCAL II - Data Structures Philip Fees CS341

CS341 PASCAL II - Data Structures

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PASCAL II - Data StructuresPASCAL II - Data Structures

Philip Fees

CS341


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Introduction Introduction

What will be studied?– Data Types– Arrays– Records– Abstract Data– Pointers– Linked lists, Stacks, Queues

What is a data structure?


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Workshop 1Workshop 1

File I/O Concepts Pascal File I/O User Defined Types


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File I/O ConceptsFile I/O Concepts

Generally termed Device I/O– Could be hard disk, CD-ROM, tape, etc.– Could be terminal, socket (IPC/Internet), etc.

Delimited files (whitespace, eol, eof) vs. non delimited

Encoded (ASCII, EBCDIC) vs. binary Open and Close Read or write via file/device handle (symbolic name) Seek vs. non-seek devices Sequential vs. Indexed


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Pascal File I/O - HandlesPascal File I/O - Handles

Identify handle (symbolic name)Program myProgram (input, output, fileHandle);

…

VARfileHandle : text;

Associate file to handle– “create procedure file prior to compiling and

running the program”– TP: assign(fileHandle,’myTextFile.txt’);


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Pascal File I/O - Open & Seek

Open the filereset(fileHandle);

rewind is part of “seeking” delimiter tests

WHILE not eol DO

WHILE not eol(fileHandle) DO

WHILE not eof DO

WHILE not eof(fileHandle) DO


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Pascal File I/O - Read & Write

Read from file via handlereadln(fileHandle, variable1, variable2, …);

Write to file via handlewriteln(fileHandle, ‘this is a test’, variable1, …);

Ease old file contentsrewrite(fileHandle);

See example pg. 444


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Exercises

Pg. 448 25 - 30


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User Defined TypesUser Defined Types

Characteristic of a data type (int, char, boolean)– set of value– fixed amount of memory

Ordinal data type have pred() and succ() values

User defined a.k.a. enumerated data type


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Enumerated Data TypeEnumerated Data Type

SyntaxType

Weekday = (Mon, Tues, Wed, Thur, Fri);

UsageVAR

Day : Weekday;

…

Day := Mon;

if (Day = Mon) then


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SubrangesSubranges

Define one type as subset of another type Examples

TYPEUSYears = 1776..1998;

Days = (Sun, Mon, Tues, Wed, Thur, Fri, Sat);

Weekdays = Mon..Fri;

Operations: succ() and pred()


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ExercisesExercises

Pg. 454-455 # 2, 15 Pg. 461 #22-26 Pg. 465 #8, 20, 21, 22


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Single Dimensional Arrays Selection Sort Arrays and Subroutines Searching Arrays


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ArraysArrays

Collection of data elements Data elements are the same type Contiguous in memory Access individuals by subscript Array size determined by:

element size * number of elements


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Pascal ArraysPascal Arrays

name : ARRAY [ index type ] OF type; Example 1:

VAR

List : ARRAY [1..5] OF integer;

Example 2:TYPE

Numbers = ARRAY [1..5] OF integer;

VAR

List : Numbers;


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Pascal Arrays (cont.)Pascal Arrays (cont.)

index type alternativesTYPE

DAYS = (SUN, MON, TUES, WED, THUR, FRI, SAT);

VAR

StockPriceList : ARRAY [9..16] OF real;

NegativeList : ARRAY [-2..3] OF char;

HoursWorked : ARRAY [MON..FRI] of real;


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Use of ConstantsUse of Constants

Good PraticeCONST

ClassSize = 35;

Type

TestScores = 0..100;

VAR

Score : ARRAY [1..ClassSize] of TestScores;


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Arrays and LoopsArrays and Loops

“Looping” over the array Example:

FOR J := 1 to ClassSize DO

BEGINwrite(‘next: ‘);

readln(Score[J]);

writeln(‘value = ‘, Score[J]);

END


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ReviewReview

Example 10.7 pg. 491 Example 10.9 pg. 493 Example 10.10 pg. 494


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Selection SortSelection Sort

Sorting a list of values Algorithm

– start with first element [1] (current)– find smallest element in array and

exchange with current– current := next array element (current + 1)– continue to end of array

What is the best and worst case?


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Arrays and SubroutinesArrays and Subroutines

See GetData example on pg. 508 Call by value vs. call by reference

– Call by value: create a copy of the array– Call by reference: refer to the passed array– Performance implications


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Search AlgorithmsSearch Algorithms

Sequential Search (pg. 526)– search entire array until value located or

“hit” the end of the array– Average of N iterations of loop

Binary Search (pg. 528)– Assumes sorted array– start in middle; look in upper or lower half– Average of log N iterations of loop


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AnalysisAnalysis

Overhead of inserting new value in sorted array

What should maximum size of the array be?

When should an array be used?


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ExercisesExercises

Arrays: pp. 497-500 # 1-5, 10, 20 Sorts: pg. 507 # 2, 3, 6 Subroutines: pg. 516 # 16-19 Searching: pg. #533 5, 15


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Multi-dimensional arrays


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Array in MemoryArray in Memory

Array stored in contiguous memory Location is calculated:

– Starting address + (row index * # of columns) + column index

Row Major vs. Column Major


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Pascal SyntaxPascal Syntax

Syntax<name> : ARRAY [ <row index>, <column

index> ] OF <element type>


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Two Dimensional ExampleTwo Dimensional Example

Example 1:VAR

Table : ARRAY [ 1..3, 1.. 4 ] OF integer; Example 2:

TYPE

Maxtrix = [ 1.. 3, 1.. 4] OF integer;

VAR

Table : Matrix;


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IterationIteration

Example:FOR row := 1 to 3 DO

FOR column := 1 to 4 DO

writeln(‘Table[‘,row,’, ‘, column,’] = ‘, Table[row][column]);


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Higher Dimensional ArraysHigher Dimensional Arrays

Syntax<identifier> : ARRAY [ A1 .. B1, A2 .. B2, …,

An .. Bn] OF <type> Example1:

cube : ARRAY [ 1..3, 1..4, 1..5] OF integer; Example 2:

cube : ARRAY [ 1..3 ] OF ARRAY [ 1..4, 1..5 ] OF integer;


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ExercisesExercises

pg. 567 # 4, 9-12, 13-15


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Records Variants Binary Files


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Sets


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Defining and DeclaringDefining and Declaring

SyntaxTYPE

<type name> = SET OF <base type> ;

VAR

<variable name> : <type name> ;

ExampleTYPE

Digits = SET OF 0..9;

VAR

numbers : Digits;


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Different than SubtypesDifferent than Subtypes

Assignmentnumbers := [ 0, 2, 4, 6, 8 ];

Set is undefined until assignment Assigned values must be in base type -

elements of the set Universal sets contain all values Subsets - one set contains all members of

another set See set definitions on top of page 735.


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Set OperationsSet Operations

Union: A + B Intersection: A * B Difference: A - B


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Relational OperatorsRelational Operators

equal: A = B sets A and B are identical not equal: A <> B set A and B are not

identical subset: A <= B A is a subset of B superset A >= B A is a superset of B

(A<=B)


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MembershipMembership

Syntax<element> IN <set>

Example2 IN numbers

Boolean value: is 2 in the numbers set?


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Membership ExampleMembership Example

Useful for “edit checks” Example

IF response IN [‘Y’, ‘y’] THEN(continue action here)

ELSE(alternative action here)

Review example on page 744.


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ExercisesExercises

Page 739 # 9-15, 26-30 Page 743 # 2, 7-20, 27 Programming Problem Page 759 # 1, 3


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Model Builder Abstract Data Type (ADT) String ADT Linked List ADT


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Model BuilderModel Builder

Model, design, or abstraction - analysis without being concern for details

Examples– World Wide Web– Windows– Virus– UNIX: parent process, child process, kill,

fork, etc.


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Abstract Data TypeAbstract Data Type

collection of data (objects) shared properties shared operations Examples: Array, Integers,


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ADT Example - StringADT Example - String

definition - finite sequence of characters terminated with null character access individual elements (substring) Operations: create, read, write, assign, length reconsider operations if string is defined by

length not null terminator.


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ADT Example - Linked ListADT Example - Linked List

Definition - list of data items associated by a link to one or more nodes.

Typically point to next node (single linked) or previous node (double linked)

Head node is first node in list To “walk” the list, must start at head and

proceed sequentially. Task: Define operations, define interfaces,

implement


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Linked Lists Array Implementation of Linked Lists Pointers Pointer Implementation of Linked Lists


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Why Linked ListsWhy Linked Lists

Arrays– Size fixed at Compile Time, inefficient space

utilization– Inserting, deleting, organizing are costly. Why?

Requirement– Size determined at Run Time– Minimal cost to insert, delete, and organize data

Examples– Sorting, data with undetermined number of items


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Linked ListsLinked Lists

Diagram data structure (See page 872) Define operations (See page 881) Define implementation base data

structures (See page 873) Diagram operation’s effect on sample

data structure (See page 887)


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Introduction to PointersIntroduction to Pointers

A pointer doesn’t contain the data, but contains a way of locating the data.

Example: Array subscriptpointer : integer

data : array [1..100] of char;

…

pointer := 5;

writeln(array[pointer]);


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Array Implementation of Linked Array Implementation of Linked ListsLists

Issues– Still have compile time limit on number of nodes,

wasted space– Which nodes are “free”

Benefits– Simple base data type– Ok if max nodes know at compile time– Still have benefits of low cost insert, update, and

organize


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Array Implementation (cont.)Array Implementation (cont.)

Free nodes– Mark all free node - sequential search– Keep linked list of free nodes

Book has special procedures to handle free nodes

Modify linked list procedures to handle free linked list– Move InitializeSpace logic into Create Procedure– Pass InsertNode the data in place of the pointer P


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Pointers & Dynamic MemoryPointers & Dynamic Memory

Declaring a pointer (see page 874)Var

intPtr : înteger;

Allocate memorynew(intPtr);

Access and deallocate memoryintPtr^ := 10;

writeln(intPtr^);

dispose(intPtr^);


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intPtr : înteger;


Access and deallocate memoryintPtr^ := 10;

writeln(intPtr^);

dispose(intPtr^);


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intPtr : înteger;


Access and deallocate memoryintPtr^ := 10;writeln(intPtr^);dispose(intPtr);


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Pointers & Dynamic Memory Pointers & Dynamic Memory (cont.)(cont.)

NIL value - doesn’t point to anything Memory allocated by new comes from heap Must deallocate via dispose Must keep track of all allocated memory -

memory leaks


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Pointer Implementation of Linked Pointer Implementation of Linked ListsLists

See page 889


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Variations on Linked ListVariations on Linked List

Dummy Header - avoid test for empty list

Circularly Linked - no NIL Doubly Linked List - don’t need previous

node


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ExercisesExercises

Pg 872 # 16 Pg 880 # 9-19

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CS341 PASCAL II - Data Structures1 PASCAL II - Data Structures Philip Fees CS341