Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps
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In this lesson, we're going to look at how to loop through a block of code using the for() iteration statement. A looping statement is very similar to other conditional statements (such as the if() statement), except at the end of its code block it loops back to the top where the initial condition is evaluated, and continues to do so until the condition evaluates as false.
For this lesson, you should create an ASP.NET project called “CS-ASP_026” and create a single resultLabel Control:
And in the Default.aspx.cs file write the following in the Page_Load() method:
And then run the application to see the result:
Let’s break down what’s happening in the for() iteration statement here:
We initialize, to zero, an int variable that is local to the for loop, called i.
We create a conditional evaluation at the start of every loop (here it checks if i is less than 10).
If the evaluation in (2) returns true, increment i by one, else end the loop.
For each time the conditional evaluates true (10 times) execute this line of code.
Perhaps the best way to illustrate how this loop executes is to set a break-point and watch it progress – line by line – in debug mode. Remember to press the F10 key to step through each part of code as it executes. Also, it would be worthwhile to pin the i variable in order to see exactly where and when it increments:
Tip:
Naming the counter variable’s as “i” is quite common throughout computer programming. It can stand for “iterator” or, when used as the index for an array could stand for “indexer.” You might also see code that uses “c”, as in “counter” or any other single-letter character. This is a coding convention that is supposed to improve readability, but you are free to use whatever convention makes most sense to you.
It may be a bit difficult, at first, for beginners to remember the exact syntax for constructing for() loops. Luckily, Visual Studio has a short-cut for creating a for() loop template by using the following sequence: type in the word “for” and on the keyboard hit the tab key twice:
This kind of preset template is called a "code snippet" and you can even find it referenced in Intellisense when typing in the for keyword:
Another shortcut you can exploit by using this code snippet is renaming the iterator variable, which then automatically renames it for the rest of the for() statement:
Tip:
There are a lot of useful code snippets you will encounter as we move forward. Eventually, you can even learn how to create your own custom code snippets!
It’s worth noting that you can, of course, (1) start with any value you want for the iterator, (2) perform any legal conditional evaluation on the iterator, and (3) perform any calculation on the iterator, as well:
One of the greatest uses of looping statements is to use the iterator as an index for an array (you will often hear this stated as “looping through an array”):
Tip:
Notice that when looping through the names[] array, we loop only when i is less than the length of the array. Why not less than or equal to? Because arrays are zero-based, whereas names.Length begins at one. If we were to use less than or equal to, we would receive an index out of range exception.
You will begin to see the power of arrays and loops when combined with all of the different ways of manipulating and sorting arrays:
A common usage for looping through an array would be to go through a database or list of items, searching for a particular item you had in mind. You might imagine that if you have a very large array of items, you would not want the loop to continue after it finds the item you are looking for. By default, that’s exactly what would happen, however, you can prematurely break-out of the loop by using the break keyword:
To show the iteration process, you can set a break-point and watch it in Debug mode, or you can add this else() clause. Notice how even though there are four items in the list the for() loop stops executing after it found the item we are looking for at the third position in the list:
Now that you know how to work with arrays and create a for loop, you should be able to see the value of using them together. Keep these techniques fresh, review what you've learned, and then move on to the next challenge. Good luck!
Lesson 1 - Series Introduction
Lesson 2 - Installing Visual Studio 2015
Lesson 3 - Building Your First Web App
Lesson 4 - Understanding What You Just Did
Lesson 5 - Working with Projects in Visual Studio
Lesson 6 - Simple Web Page Formatting in Visual Studio
Lesson 7 - Variables and Data Types
Lesson 8 - Data Type Conversion
Lesson 9 - Arithmetic Operators
Challenge 2 - ChallengeSimpleCalculator
Solution - ChallengeSimpleCalculator
Lesson 11 - Conditional If Statements
Lesson 12 - The Conditional Ternary Operator
Challenge 3 - ChallengeConditionalRadioButton
Solution - Challenge Conditional RadioButton
Lesson 13 - Comparison and Logical Operators
Lesson 13 Challenge - First Papa Bob's Website
Solution - Challenge First Papa Bob's Website
Lesson 14 - Working with Dates and Times
Lesson 15 - Working With Spans of Time
Lesson 16 - Working with the Calendar Server Control
Challenge 4 - Challenge Days Between Dates
Solution - Challenge Days Between Dates
Lesson 17 - Page_Load and Page.IsPostBack
Lesson 18 - Setting a Break Point and Debugging
Lesson 19 - Formatting Strings
Challenge 5 - Challenge Epic Spies Assignment
Solution - Challenge Epic Spies Assignment
Lesson 20 - Maintaining State with ViewState
Lesson 21 - Storing Values in Arrays
Lesson 22 - Understanding Multidimensional Arrays
Lesson 23 - Changing the Length of an Array
Challenge 6 - Challenge Epic Spies Asset Tracker
Solution - Challenge Epic Spies Asset Tracker
Lesson 24 - Understanding Variable Scope
Lesson 25 - Code Blocks and Nested If Statements
Lesson 26 - Looping with the For Iteration Statement
Challenge 7 - Challenge For Xmen Battle Count
Solution - Challenge For Xmen Battle Count
Lesson 27 - Looping with the while() & do...while() Iteration Statements
Lesson 28 - Creating and Calling Simple Helper Methods
Lesson 29 - Creating Methods with Input Parameters
Lesson 30 - Returning Values from Methods
Lesson 31 - Creating Overloaded Methods
Lesson 32 - Creating Optional Parameters
Lesson 33 - Creating Names Parameters
Lesson 34 - Creating Methods with Output Parameters
Challenge 8 - Challenge Postal Calculator Helper Methods
Solution - Challenge Postal Calculator Helper Methods
Solution - Mega Challenge Casino
Lesson 35 - Manipulating Strings
Challenge 9 - Phun With Strings
Solution - Challenge Phun With Strings
Lesson 36 - Introduction to Classes and Objects
Challenge - Hero Monster Classes Part 1
Solution - Hero Monster Classes Part 1
Challenge - Hero Monster Classes Part 2
Solution - Challenge Hero Monster Classes Part 2
Lesson 37 - Creating Class Files Creating Cohesive Classes and Code Navigation
Lesson 38 - Understanding Object References and Object Lifetime
Lesson 39 - Understanding the .NET Framework and Compilation
Lesson 40 - Namespaces and Using Directives
Lesson 41 - Creating Class Libraries and Adding References to Assemblies
Lesson 42 - Accessibility Modifiers, Fields and Properties
Lesson 43 - Creating Constructor Methods
Lesson 44 - Naming Conventions for Identifiers
Lesson 45 - Static vs Instance Members
Challenge 10 - Challenge Simple Darts
Solution - Challenge Simple Darts
Lesson 46 - Working with the List Collection
Lesson 47 - Object Initializers
Lesson 48 - Collection Initializers
Lesson 49 - Working with the Dictionary Collection
Lesson 50 - Looping with the foreach Iteration Statement
Lesson 51 - Implicitly-Typed Variables with the var Keyword
Challenge 11 - Challenge Student Courses
Solution - Challenge Student Courses
Lesson 53 - Working with Enumerations
Lesson 54 - Understanding the switch() Statement
Lesson 55 - First Pass at the Separation of Concerns Principle
Lesson 56 - Understanding Exception Handling
Lesson 57 - Understanding Global Exception Handling
Lesson 58 - Understanding Custom Exceptions
Lesson 59 - Creating a Database in Visual Studio
Lesson 60 - Creating an Entity Data Model
Lesson 61 - Displaying the DbSet Result in an ASP.NET GridView
Lesson 62 - Implementing a Button Command in a GridView
Lesson 63 - Using a Tools-Centric Approach to Building a Database Application
Lesson 64 - Using a Maintenance-Driven Approach to Building a Database Application
Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database
Lesson 66 - Package Management with NuGet
Lesson 67 - NuGet No-Commit Workflow
Lesson 68 - Introduction the Twitter Bootstrap CSS Framework
Lesson 69 - Mapping Enum Types to Entity Properties in the Framework Designer
Lesson 70 - Deploying the App to Microsoft Azure Web Services Web Apps
Papa Bob's Mega Solution Part 1 - Setting up the Solution
Papa Bob's Mega Solution Part 2 - Adding an Order to the Database
Papa Bob's Mega Solution Part 3 - Passing an Order from the Presentation Layer
Papa Bob's Mega Solution Part 4 - Creating the Order Form
Papa Bob's Mega Solution Part 5 - Adding Enums
Papa Bob's Mega Solution Part 6 - Creating an Order with Validation
Papa Bob's Mega Solution Part 7 - Calculating the Order Price
Papa Bob's Mega Solution Part 8 - Displaying the Price to the User
Papa Bob's Mega Solution Part 9 - Creating the Order Management Page