1 Working with Data Structures Kashef Mughal

2 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++

3 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

4 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

5 One-Dimensional Array AlaskaMontanaSouth CarolinaTennesseeTexas Alaska Montana South Carolina Tennessee Texas

6 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

7 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}

8 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 ”

9 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

10 Array Properties and Methods ClearSets a range of elements in the Array to zero or to a null reference (Nothing in Visual Basic). CopyCopies a section of one Array to another Array LengthReturns the size of the array UBoundReturns the upper bound (index) for the given array. Also GetUpperBound is the same LBoundReturns the lower bound (index) for the given array. Also GetLowerBound is the same SortSorts the elements in Array

11 In-class Assignments  Try the following Exercises  Pages  Pages  Page  Page 260  Page 263  Take a break when done

12 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

13 Two-Dimensional Arrays  A two-dimensional array resembles a table in that the variables are in rows and columns AC24ShirtRed BD12CoatBlue CP14BlouseWhite strProducts(0, 0)strProducts(0, 2) strProducts(2, 1) strProducts(1, 2)

14 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

15 Other Data Structures  Constants  Enumerations  Structures  ArrayList  Collections  Hashtable

16 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

17 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

18 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

19 In-class Assignments  Try the following Exercises  Pages  Pages  Page 234  Page 236  Pages  Take a break when done

20 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

21 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

22 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

23 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

24 In-class Assignments  Try the following Exercises  Page 247  Page 248  Page 251  Page 254  Next week Chapter 7 and Review