Lesson 23 - Changing the Length of an Array

Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps

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This lesson covers how to change the length of an array. Arrays are immutable by default, which means that once you define or declare an array, just like a variable, you normally cannot increase or reduce the number of array elements. Returning to a previous analogy, you cannot remove or add any more “buckets” strung up on the “broomstick”; it is of fixed size once that size is declared. We imprint on the broom-handle the size as precisely five elements:

cs-asp-023---changing-the-length-of-an-array.001

Fortunately, the .NET framework class library defines arrays with some helper methods that can process the array, and return one with a new size – returning an array that is either larger or smaller than the original array. You can also access other helper methods that get the sum, minimum, maximum, and average values within the array, along with other generally useful operations.

Step 1: Create a New Project

Let’s begin this lesson by creating a new ASP.NET project called “CS-ASP_023” and create the following Controls and programmatic IDs:

  1. hoursTextBox

  2. addButton

  3. resultLabel

cs-asp-023---changing-the-length-of-an-array.002

Step 2: Begin Coding a Simple Work Calculator

This application will be a simple calculator that allows us to add the number of work hours on a given project and return some statistics. Each work session will be stored in an array, so one session might be eight hours, another is four hours, and another is six hours. Those would be three different sessions. From that, we can access array helper methods to average them out and find the session with the most hours, the fewest hours, the average session length, and so on.

Let’s first create the array with zero elements (to start off with) upon page load, and add it to the ViewState:

cs-asp-023---changing-the-length-of-an-array.003

Step 3: Array Resizing Magic with Array.Resize()

Then, in the addButton_Click event create another locally scoped variable called hours and populate it with all of the previously added elements preserved in ViewState. Remember that the ViewState["Hours"] is a generic object and therefore needs to be cast to an array of doubles.

Then resize the hours array (adding one more element) by passing it into the Resize() helper method found in the Array class. Note that the Resize() method takes in the current hours array, as well as its current length, plus one:

cs-asp-023---changing-the-length-of-an-array.004

The ref keyword here means “reference” and essentially takes the actual variable/object hours into the Resize() method rather than just copying it. This means you can perform an operation on the variable and not have to return a copy of it back to the original variable. There will be a lot more said about passing by reference/value in further lessons.

It’s worth noting that the Array.Resize() method doesn’t violate the fundamental rule of array immutability. What the method actually does – behind the scenes – is make a new array with one more element than the one we passed into it (in this case hours), and then copies all of the elements from the one we passed in, into the new array.

Tip:

Here’s a concept that may help you wrap your head around how Array.Resize() works: if you’re a Star Trek fan, you may be familiar with the concept of teleportation used throughout the series. With teleportation, no object actually moves from one place to another, but rather each particle (and its position in space) making up the source object gets copied (you can even imagine that the teleportation device uses three-dimensional arrays to represent each particle in three-dimensional space). A new object is simply built off of that copied information at the destination.

Step 4: Find the Highest Index in the Array with GetUpperBound()

After that code, we will want to (1) return the highest numerical index in the hours array. And, since we know in advance that it will be the newest array element added in Array.Resize() – reference that index number (2) to store whatever the user entered in hoursTextBox.Text:

cs-asp-023---changing-the-length-of-an-array.007

Tip:

GetUpperBound() takes in the dimension of the current array that you are evaluating. Remember in the previous lesson we discussed multi-dimensional arrays, but in this case our array only has one dimension. Therefore, we pass in 0, since the arrays' indexes are zero-based.

And then simply replace the previous values in ViewState[“Hours”] with the new hours array, and then output the sum of all array elements:

cs-asp-023---changing-the-length-of-an-array.008

When you run the application, you will now be able to add hours and store them in ViewState in between PostBack’s:

cs-asp-023---changing-the-length-of-an-array.009


cs-asp-023---changing-the-length-of-an-array.010

Step 5: Some More Helper Methods Available to Arrays

We can also call several other helper methods available to the array:

cs-asp-023---changing-the-length-of-an-array.011

When you run the application, you will now see these various statistics. Here, we entered three values (6, 7, and 9) to represent the hours worked in three different sessions:


cs-asp-023---changing-the-length-of-an-array.012


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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