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Working with Data Structures

Kashef Mughal

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Chapter 5

Please review on your own

A few terms

.NET Framework - programming model

CLR (Common Language Runtime) - compiles the code written in all the .NET languages

Bottom line - With .NET Microsoft wants to compete with other Object Oriented languages like JAVA, C++

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Arrays

An array is a group of variables that have the same name and data type and are related in some way

Array is really a list that holds similar data e.g. employee lastnames

Although arrays in Visual Basic .NET can have as many as 60 dimensions, the most commonly used arrays are one-dimensional and two-dimensional

Programmers use arrays to store related data in the internal memory of the computer

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One-Dimensional Arrays

A one-dimensional array is simply a row (or column) of variables

A two-dimensional array resembles a table in that it has rows and columns

Each element in an array is identified by a subscript or index, which Visual Basic .NET assigns to the variable when the array is created

You refer to an array element by the array’s name followed by the element’s index

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One-Dimensional Array

Alaska Montana South Carolina Tennessee Texas

Alaska

Montana

South Carolina

Tennessee

Texas

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Declaring an Array

Basic Syntax accessibility arrayname() As datatype =

{initialValues} accessibility is Dim, Public, or Private These statements create and initialize the array

variables in memory In VB.NET arrays are zero based meaning the first

item in the array has a 0 index

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Declaring an array - Examples

Dim strCitys(3) As String

Private intNumbers(5) As Integer

Private udtItems(4) As ItemStruc

Private strStates() As String = {“Hawaii”, “Alaska”, “Maine”}

Dim intScores() As Integer = {75, 9, 23, 6}

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Storing Data in a an Array

You can use a variety of ways to enter data into an array

strMonthArray(0) = “Jan”

strMonthArray(1) = “Feb”

strMonthArray(2) = “Mar”

strMonthArray(3) = “Apr”

strMonthArray(4) = “May”

strMonthArray(5) = “June”

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Display the Contents of a an Array

You can use For .. Next loop to display an Array

or to search for a value

Dim strMonths() As String = {“JAN”, “FEB”, “MAR”, “APR”,

“MAY”, “JUN”}

Dim intX As Integer

For intX = 0 To strMonths.Length - 1

Me.MonthListBox.Items.Add(strMonths(intX))

Next intX

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Array Properties and Methods

Clear Sets a range of elements in the Array to zero or to a null reference (Nothing in Visual Basic).

Copy Copies a section of one Array to another Array

Length Returns the size of the array

UBound Returns the upper bound (index) for the given array. Also GetUpperBound is the same

LBound Returns the lower bound (index) for the given array. Also GetLowerBound is the same

Sort Sorts the elements in Array

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In-class Assignments

Try the following Exercises Pages 212 - 214 Pages 215 - 216 Page 217 - 222 Page 260 Page 263 Take a break when done

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Misc. Array Topics

The ReDim statement is used to change the size of one or more dimensions of an array that has already been formally declared

The ReDim statement can appear only at procedure level. This means you can redefine arrays inside a procedure but not at class or module level.

Use the Preserve keyword with the ReDim to save the contents of existing array

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Two-Dimensional Arrays

A two-dimensional array resembles a table in that the variables are in rows and columns

AC24 Shirt Red

BD12 Coat Blue

CP14 Blouse White

strProducts(0, 0) strProducts(0, 2)

strProducts(2, 1)

strProducts(1, 2)

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How would you initialize a Two-Dimensional Array

Lets say we are working with an array that is 4*2. We could use the following code to initialize the values We are using next For .. Loops here

dim intRow, intColumn as integer

dim intScores

For intRow = 0 To 3

For intColumn = 0 To 1

intScores(intRow, intColumn) = 0

Next intColumn

Next intRow

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Other Data Structures

Constants Enumerations Structures ArrayList Collections Hashtable

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Constants

Constants store values that, as the name implies, remain constant throughout the execution of an application.

Using constants allows you to provide meaningful names instead of numbers, making your code more readable.

Examples of constants are values like Pi, location of a file that does not change

Public Const pi As Single = 3.14

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Enumerations

Enumerations provide a convenient way to work with sets of related constants

In addition they let you associate constant values with names.

For example, you can declare an enumeration for a set of integer constants associated with the days of the week, and then use the names of the days rather than their integer values in your code

The only data types allowed are integer, long, short and byte

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Structure

You can combine data items of different types to create a structure.

A structure associates one or more members with each other and with the structure itself.

When you declare a structure, it becomes a composite data type, and you can declare variables of that type.

Structures are useful when you want a single variable to hold several related pieces of information. E.g. you might want to keep an employee's name, telephone extension, and salary together

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In-class Assignments

Try the following Exercises Pages 223-228 Pages 230-232 Page 234 Page 236 Pages 238-245 Take a break when done

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ArrayList

ArrayList is a form of an array that is easier to use

Think of an ArrayList as a resizable one-dimensional array of objects.

In addition to automatic resizing, ArrayList has a few other advantages over Array.

ArrayList has methods that will add, insert, and remove a range of elements

ArrayList does not need the index like an array does

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Collections

Collection object gives you a way to refer to a related group of items as a single object.

Collections are used a lot by VB itself (components in a project, for example, are a collection) and are pretty flexible.

The members in a collection don't even have to be the same data type

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Hashtable

Hashtable is a special kind of collection

The Hashtable collection type stores key-value pairs and allows you to locate items in the collection based on the key

Similar in principle to a primary key in a database table

The advantage is that we do not need an index to locate the item

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Midterm

On 2/11 Chapter 1-7 In-class material Closed Book 100 questions

true/false multiple choice

200 points 2 hours Grades right now

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In-class Assignments

Try the following Exercises Page 247 Page 248 Page 251 Page 254 Next week Chapter 7 and Review