INT422 Internet III Web Programming on Windows

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INT422 Internet III Web Programming on
Windows

• Arrays and Collections

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Arrays
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Arrays

• Named data storage structure
• Multiple elements
• Zero-based
• A 10-element array of strings is declared
  asstring studentNames new string10
• Data type is up to you integer, string, or
  object

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Arrays declaring and using

• Declare string array with 5 elements
• //Build an array of five strings
• //Remember - .NET indexes are zero-based
• //Array elements start at index 0
• string sa new string5
• int i 0
• for(i 0 ilt 5 i)
• sai "Element " i.ToString()

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Arrays declaring (continued)

• Another syntax
• 'Build an array of five strings
• 'Remember - .NET indexes are zero-based
• 'Array elements start at index 0
• string sa new string5
• "Zero, "One, "Two, "Three, Four

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Collections
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Collections

• Collection is a generic data container
• A group of related similarly typed objects
• Collections store objects dynamically in memory
  and can grow or shrink at run-time
• Used frequently throughout the BCL
• Various types of Collections are defined in the
  System.Collections namespace
• Tip Collections offer more power and efficiency
  than Arrays for many common tasks

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Collections - contents

• Collections contain other objects
• Since everything is an Object in .NET, everything
  can be placed in a Collection, including
  Integers, Strings, objects, or even other
  collections

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Collections examples

• Examples
• Controls collection the collection of all the
  Control objects that appear in a form
• ListItems collection the collection of all the
  ListItem objects that appear in a list (e.g.
  drop-down list)
• TableRow collection the collection of all the
  TableRow objects that appear in a data table

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Methods supported by collections

• Collections support a number of easy-to-use and
  common methods and properties
• For the examples that follow, assume that a
  drop-down list control called ddlcourses
  exists, n is an integer var, and name is a
  string var
• Examples
• Add ddlcourses.Items.Add(INT422)
• Count n ddlcourses.Items.Count.ToString()
• Clear ddlcourses.Items.Clear()
• SelectedItem name ddlcourses.SelectedItem.Text
  

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Why do we need to know this?

• Many of the controls on the ASP.NET user
  interface are list controls
• A list control is a collection of list item
  objects
• You typically build list items programmatically
  from values you calculate, or from values you get
  from a data file, or a database

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Example create a course list

• Heres an example that creates a list of courses
  programmatically (the name of the drop-down list
  control is ddlCourses)
• //Build the ddlCourses drop-down list
• ddlCourses.Items.Add("INT422")
• ddlCourses.Items.Add("DCN455")
• ddlCourses.Items.Add("EAC397")
• ddlCourses.Items.Add("SYS466")
• ddlCourses.Items.Add("JAC444")

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Example create a list of file names

• Heres an example that creates a list of file
  names found in the C\TEMP folder (the name of
  the drop-down list control is ddlFiles you
  will learn about file I/O soon)
• string files Directory.GetFiles("c\temp")
• foreach(string filename in files)
• ddlFiles.Items.Add(filename)