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Using loops

From: ASP.NET Essential Training

Video: Using loops

Both Visual Basic and C# support the concept of looping, executing a bit of code multiple times depending on a particular condition. I'll demonstrate two kinds of loops. For loops and While loops in both languages, starting in C#. I will open the file ProgrammingCSharp. aspx and then I'll save the file under a new name of LoopingCSharp.aspx. A For loop is a loop that executes multiple times and uses a numeric value so that you can increment the value or decrement it each time through the loop. In C# you use a For loop by creating keyword for and then starting with an opening parenthesis you put in three expressions separated with semicolons.

Using loops

Both Visual Basic and C# support the concept of looping, executing a bit of code multiple times depending on a particular condition. I'll demonstrate two kinds of loops. For loops and While loops in both languages, starting in C#. I will open the file ProgrammingCSharp. aspx and then I'll save the file under a new name of LoopingCSharp.aspx. A For loop is a loop that executes multiple times and uses a numeric value so that you can increment the value or decrement it each time through the loop. In C# you use a For loop by creating keyword for and then starting with an opening parenthesis you put in three expressions separated with semicolons.

The first expression declares a variable and sets its initial value. I'll create an integer variable named counter and set its initial value to 1. Then, after a semicolon I put in a Boolean expression. This expression will be evaluated each time through the loop and as long as it's true the loop will continue. When the expression is false, the loop will terminate and the code will jump to after the loop. I'll use the expression counter < 3. Then finally after the second semicolon you say what you want to do each time through the loop and I'll use an increment operator, the ++ operator which means add one to the current value of that variable. After the For declaration you put in a pair of braces and any code that place between the braces, the code block will be executed once for each time through the loop.

I will use the output function that I've already created and I'll output the value, the value of counter is, and then I'll append the value of the variable using the + operator, which in C# is how you concatenate values together. I'll save and test the page. I'll select Debug > Start without Debugging. When the page opens I'll click the Run Code button and you will that I output the value of counter twice. When the value of the variable matches 3 though, the loop is terminated. So that's how you create a For loop.

Now let's take a look at how to create a While loop. I'll press Alt+Shift+Enter to expand to full screen, so I can see all of the codes. I'll place the While loop after the For loop. I would like to use the same variable. That is, the counter variable, but right now the counter variable is going to expire when the For loop is completed. In the .NET Framework when you declare a variable inside a looping construct, it means that; that variable expires when the code block expires. I'll fix this by moving the declaration of the counter variable above the for block.

Notice I'm not setting its defaulted value; I'm only declaring it. Then I'll go down to the for block and remove the data type from the variable declaration. Now I'm just using the variable that was already declared and the variable will still be available after the For loop is complete. I will move the cursor after the For loop and I'll put in a While loop. In a While loop you place a Boolean expression between a pair of parenthesis. I'll set my Boolean expression to a value of counter > 0, meaning that I'm going to loop as long as counter is at least 1. Then I'll copy and paste the output call. So I'm outputting the value of the counter and then, this is very important, you are responsible for changing the value of the variable. If you forget the next step, you will have created an infinite loop.

That is there is nothing in the While construct to actually change the value of the expression or the variable. So each time through the loop I'll use the expression counter -- meaning decrement the value by one. I'll save the changes and I'll run the page. When I run the code, I start off in the For loop going up by one. When I hit the value of 3, the For loop terminates and then I get into the While loop and I walk back down the values 3, 2, and 1.

So that's looping in C#. Now let's do the same thing in Visual Basic. I'll open the file ProgrammingVB.aspx, I'll save the file as LoopingVB.aspx and then I'll create the same sort of code, just in the C# version. I'll start by declaring the variable. I'll use the Dim keyword and then counter As Integer. Now I'll be able to use that variable in both the For loop and in the While loop. Here is the syntax for a Visual Basic For loop. You start off with the keyword For. Notice that the initial character is uppercase in the Visual Basic. Then the variable name and then the initial value with the assignment operator, the equal sign. Then you put in the to keyword and indicate how high you want to count.

When I press Enter, Visual Web Developer automatically puts in the keyword Next. In a For loop you start off with a For declaration and you end with a next declaration. Now I'll call my output function. Once again I'll start will a literal value and then I'm going to concatenate the value, which in Visual Basic is done with the ampersand character. So that's the completed For loop. Now I'll do the While loop. The While loop starts off with the keyword while and I'll use a Boolean expression as in the C# version where I'm looping as long as the counter is greater than 0. A While loop ends with the construct End While. Now I'll once again copy and paste my output command. I'll select the command, press Ctrl+C, place the cursor within the While loop and press Ctrl+V and then again in a While loop you are responsible for modifying the counter and in Visual Basic you can't use those simple increment and decrement operators of ++ and --.

So instead you say counter = counter - 1. So there is your For loop and your While loop in Visual Basic. I'll run the page selecting Debug > Start without Debugging. I'll click the Run Code button and there is the result in Visual Basic. So the capabilities and functionalities of the languages is the same, but the syntax that you use is different between Visual Basic and C#.

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This video is part of

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ASP.NET Essential Training

79 video lessons · 49878 viewers

David Gassner
Author

 
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  1. 18m 44s
    1. Welcome
      1m 42s
    2. Prerequisites
      2m 21s
    3. Using the exercise files
      1m 32s
    4. Upgrading exercise file websites for ASP.NET 4.5 (NEW)
      2m 40s
    5. What's new in ASP.NET 4 (NEW)
      3m 48s
    6. What's new in ASP.NET 4.5 (NEW)
      3m 23s
    7. What's new in this course update (NEW)
      3m 18s
  2. 33m 34s
    1. Understanding how ASP.NET works
      5m 52s
    2. Installing Microsoft Visual Web Developer 2008
      3m 43s
    3. Installing Visual Studio Express 2012 for web (NEW)
      2m 12s
    4. Hello World: Creating your first ASP.NET web site
      4m 28s
    5. Creating pages with dynamic output
      7m 39s
    6. Understanding the development web server
      4m 49s
    7. Exploring the development environment
      4m 51s
  3. 40m 2s
    1. Understanding Microsoft SQL Server
      5m 47s
    2. Installing SQL Server Express
      6m 51s
    3. Exploring SQL Server Management Studio Basic
      4m 23s
    4. Creating a new database
      8m 51s
    5. Connecting to the database in ASP.NET
      5m 35s
    6. Testing SQL queries
      3m 53s
    7. Presenting a dataset in an ASP.NET page
      4m 42s
  4. 25m 31s
    1. Understanding ASP.NET web form pages
      5m 51s
    2. Separating presentation and logic with code files
      4m 17s
    3. Adding web form controls to a page
      5m 25s
    4. Handling postback data in a web form page
      5m 50s
    5. Using data binding expressions
      4m 8s
  5. 48m 37s
    1. Creating a testing environment
      4m 40s
    2. Declaring and using a simple variable
      6m 14s
    3. Declaring and using a complex object
      6m 16s
    4. Using loops
      6m 52s
    5. Using functions
      9m 25s
    6. Using trace statements
      4m 47s
    7. Debugging with breakpoints
      5m 45s
    8. Commenting code
      4m 38s
  6. 17m 43s
    1. Creating web controls
      5m 53s
    2. Registering a user control on a web form page
      3m 25s
    3. Registering controls globally in the web.config file
      3m 53s
    4. Adding public properties to a web control
      4m 32s
  7. 19m 7s
    1. Understanding Cascading Style Sheets (CSS)
      5m 36s
    2. Attaching external CSS files
      3m 12s
    3. Defining a CSS selector
      6m 10s
    4. Using CSS class selectors in server controls
      4m 9s
  8. 30m 34s
    1. Presenting data with the GridView control
      5m 49s
    2. Controlling GridView paging and appearance
      5m 46s
    3. Editing data with the GridView control
      6m 57s
    4. Presenting data with the DataList control
      5m 42s
    5. Formatting data with binding expressions
      6m 20s
  9. 36m 46s
    1. Using the DetailsView control
      7m 33s
    2. Inserting data with the DetailsView control
      6m 36s
    3. Redirecting page requests
      9m 39s
    4. Creating an update page
      6m 20s
    5. Linking to update pages from the list page
      4m 3s
    6. Deleting database records
      2m 35s
  10. 22m 15s
    1. Customizing forms with item editing templates
      6m 7s
    2. Adding validator controls to a form
      6m 40s
    3. Controlling the validation error message display
      6m 24s
    4. Using the ValidationSummary control
      3m 4s
  11. 29m 49s
    1. Creating a query with joined tables
      8m 6s
    2. Replacing control style properties with CSS
      5m 50s
    3. Creating a CSS file for printing
      3m 14s
    4. Suppressing elements in printed web pages
      5m 47s
    5. Selecting data for a report
      6m 52s
  12. 11m 14s
    1. Understanding ViewState and managing postbacks
      4m 36s
    2. Using session variables
      6m 38s
  13. 20m 57s
    1. Turning on forms authentication
      1m 51s
    2. Creating a page to log in users
      4m 18s
    3. Creating a page to set up new users
      4m 6s
    4. Understanding the security database
      3m 27s
    5. Configuring security in the web.config file
      2m 59s
    6. Creating a page to log out users
      4m 16s
  14. 27m 56s
    1. Installing IIS on Windows XP
      6m 32s
    2. Installing ASP.NET 3.5 on Windows XP
      1m 39s
    3. Deploying a site on Windows XP
      5m 9s
    4. Installing Information Internet Services (IIS) on Windows Vista, Windows 7, and Windows 8
      1m 56s
    5. Configuring ASP.NET 3.5 on Windows Vista
      2m 15s
    6. Deploying an application on Windows Vista
      3m 29s
    7. Scripting a database for deployment
      3m 36s
    8. Exporting database scripts in SQL Server Management Studio 2012 (NEW)
      3m 20s
  15. 2m 0s
    1. Where to go from here
      2m 0s

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