Lesson 26 - Looping with the For Iteration Statement

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.

Step 1: Create a New Project

For this lesson, you should create an ASP.NET project called “CS-ASP_026” and create a single resultLabel Control:


cs-asp-026---looping-with-the-for-iteration-statement.001


And in the Default.aspx.cs file write the following in the Page_Load() method:


cs-asp-026---looping-with-the-for-iteration-statement.002


And then run the application to see the result:


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Step 2: Breaking Down the for() Iteration Statement

Let’s break down what’s happening in the for() iteration statement here:

  1. We initialize, to zero, an int variable that is local to the for loop, called i.

  2. We create a conditional evaluation at the start of every loop (here it checks if i is less than 10).

  3. If the evaluation in (2) returns true, increment i by one, else end the loop.

  4. For each time the conditional evaluates true (10 times) execute this line of code.


cs-asp-026---looping-with-the-for-iteration-statement.004


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:


cs-asp-026---looping-with-the-for-iteration-statement.005


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.

Step 3: Code Snippets for Recalling Syntax

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:


cs-asp-026---looping-with-the-for-iteration-statement.008


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:


cs-asp-026---looping-with-the-for-iteration-statement.009


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:


cs-asp-026---looping-with-the-for-iteration-statement.010


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!

Step 4: Setting Up the Iterator

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:


cs-asp-026---looping-with-the-for-iteration-statement.012


cs-asp-026---looping-with-the-for-iteration-statement.013


Step 5: Using for() Loops with Arrays

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”):


cs-asp-026---looping-with-the-for-iteration-statement.014


cs-asp-026---looping-with-the-for-iteration-statement.015


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:


cs-asp-026---looping-with-the-for-iteration-statement.016


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Step 6: Breaking Out of the Loop

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:


cs-asp-026---looping-with-the-for-iteration-statement.018


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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:


cs-asp-026---looping-with-the-for-iteration-statement.020


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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!


Related Articles in this Tutorial:

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

Challenge 1

Solution 1

Lesson 7 - Variables and Data Types

Lesson 8 - Data Type Conversion

Lesson 9 - Arithmetic Operators

Lesson 10 - C# Syntax Basics

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

Mega Challenge Casino

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

Mega Challenge War

Solution - Mega Challenge War

Lesson 52 - Creating GUIDs

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 Challenge

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


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