Lesson 27 - Looping with the while() & do...while() Iteration Statements

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

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In this lesson, you will learn about the while() and do…while() iteration statements. These statements operate in much the same way that for() statements operate. The main difference is that a for() statement is best used when there are a particular number of iterations needed through a code block, whereas while() and do…while() are best used when a single expression needs to be evaluated and continuing the loop so long as it evaluates as true.

Step 1: Understanding Syntax for while() and do…while()

Here is the basic syntax for constructing a while() loop (you can insert any expression that evaluates to a boolean value):


Meanwhile, a do…while() loop operates in the same way, except that it’s inverted. In other words, it first executes the code block (at least once), and continues to execute so long as the evaluation holds true:


It will not be immediately apparent why do…while() is ever needed. Although it is not as commonly used as the while() loop, it is very useful when a block of code has to execute at least once, but possibly several more times.


As with the for() loop code snippet, you can quickly set up a while(), or do…while() template. Just type in “while” or “do”, respectively, and then hit the tab key twice.

Step 2: Create a New Project for a Hero vs Monster Game

Let’s begin the lesson by setting up an ASP.NET project called “CS-ASP_026” with a single resultLabel Control:


In Default.aspx.cs write some preliminary code for the Page_Load() method that sets the scene for a text-based adventure “game” between a hero and a monster:



Step 3: Simulating Game Battle Logic

Now, let’s write our “battle” logic that allows each side to duke it out, repeatedly, until one of the opponents reaches zero health. Here, each opponent deals a random amount of damage (between 1 and 10 for the hero, and between 1 and 20 for the monster):


Now, you will want to report the actual damage done for each round (try both, ++round and round++ to see the difference between the two):



The String.Format() method might look a bit strange here ,but remember you can use whatever whitespace you want in order to make the code more readable.

When you run the application, you will see the result of this epic battle. However, you will probably notice that most of the time the hero gets in a single shot – from the initial “bonus” attack - and wins without triggering the main battle logic in the while() loop. This is because the monster’s battle logic is included in the while() loop, and because it executes only when both combatants have more than zero health, the monster will often be left unable to retaliate. What we will want to do instead is have both combatants engage each other at least once so that the monster gets at least a single shot in. All we need to implement this is simply invert the while() loop so that its code block executes first, creating a do…while() loop, instead:


Now, we see that the monster gets in at least one attack every time, even if he’s at below zero health. This is because the do... while will always run the code block at least once, then it will evaluate whether the condition is true, and if the loop should continue:



As usual, you can learn a lot about the flow of execution in your code by setting a break-point and watching the magic happen in Debug mode. Try doing this for both while() and do…while() loops to see the difference between how they execute.

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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