Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps
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This lesson will cover the out keyword that is used alongside ordinary input parameters in order to output a value other than the return value. We already saw it used in a previous lesson that called the double.TryParse() method where we witness how the output parameter sent a value back out of the method, similar to the way a return value works but with a twist.
You should create a project for this lesson based on where we left off with the previous lesson, and call it “CS-ASP_034”. In the previous lesson we had a method called performAttack() that held most of the battle code. In this lesson, we will want to replace it with a new method called defeatEnemy() that functions a bit differently. Here we see that the method still performs the main battle algorithm, but it also returns a bool depending on whether or not the enemy has zero or less remaining health:
Suppose that you want the defeatEnemy() method to also return the defender’s health. Since we’re only allowed a single method return value, the best way around this is to have the defender’s health value come back out as an out parameter:
Now you can reference this method within a conditional statement and perform some sort of action depending on the returned value:
And now create the lootEnemy() method, which simply displays a message through resultLabel.Text:
It may not be clear why the out keyword is needed here. The way that input parameters normally work is that local variables provided as input at method calls have their values copied into the local input parameter and so there is no reference retained back to the original variable where the value was copied from. Whatever information is processed in the method is local to the method itself, unless it comes back out as a returned value, or an output parameter.
Tip:
You can almost think of methods as being their own little “universe” that may hold copies of variables from another “universe,” supplied via input parameters. And the only way that a method can “talk back” to the world it copied information from is via the return, out and ref keywords, or else if there is a class-level variable referenced in the method. Otherwise, a method’s internals are completely sealed off from its surroundings. Also, note that although the out keyword can solve a variety of problems, it is not very common, and should be used sparingly considering that it can be seen as violating the principle of “Single Responsibility.”
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