Lesson 25 - Code Blocks and Nested If Statements

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

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This lesson will look closer at the related topics of code blocks and nested statements.

Step 1: Create a New Project

Let’s start by creating a new ASP.NET project called “CS-ASP_025” with the following Controls and programmatic IDs:

  1. firstCheckBox

  2. secondCheckBox

  3. thirdCheckBox

  4. addButton

  5. resultLabel


cs-asp-025---code-blocks-and-nested-statements.001


In the Default.aspx.cs file, write the following code:


cs-asp-025---code-blocks-and-nested-statements.002


Here we see seven separate code blocks. The outer-most code block (1) is the namespace, which immediately holds (2) a single block of code – a class – which is called Default. The class level then immediately holds two method code blocks named (3) Page_Load and (4) addButton_Click. Finally, addButton_Click code block then holds a series of nested if() statements (5), (6) and (7). Notice, also, how you can expand and collapse the individual blocks/nested statements by clicking on the boxes with dashes in them (highlighted in green).

Tip:

Up to this point, we have been referring to the named code blocks that determine behavior for Server Controls as events. However, technically these code blocks are methods, and methods can subscribe to special kinds of properties called events. All of the methods we have been writing code into, thus far, happen to subscribe to events. This will be clarified in further lessons covering methods and events.

Step 2: Avoiding Excessive Nesting with the Return Keyword

Nested if() statements are somewhat different from the containment relationships seen in the other code blocks. They are simply used to perform logical branching in your code – as seen in previous lessons – and should be nested no more than a few levels deep. The reason for this is that it can make code look very messy and difficult to read, and there are often ways to solve the problem with other techniques. For instance, here is another way of determining whether or not all of the CheckBoxes are checked, and displaying the resultLabel only when they are:


cs-asp-025---code-blocks-and-nested-statements.005


This solves the problem in a much cleaner way since the return keyword effectively exits out of further execution for this method when any of the CheckBoxes are not checked. This provides the same functionality as the nested if() statements displaying the resultLabel message only when all CheckBoxes are checked.

Step 3: Avoiding Nesting with Compound Expressions

Another, simpler, way of solving this problem is to make a compound expression within a single if() statement, like this:


cs-asp-025---code-blocks-and-nested-statements.006


Tip:

Although this compound expression within a single if() statement is logically equivalent to the nested if() statements, there are some cases where you can’t simplify in such a way. For example, if you needed different code to execute for each condition (or, each CheckBox in this example), you would definitely need those contingencies to exist on their own “branch” of code.

In upcoming lessons we will look at looping conditional statements that can often take on deep nesting structures. However even in this case there are ways to reduce the visual impact of deep nesting by breaking up nested code and putting it into helper methods, for example.

The main takeaway from this lesson is this: Understanding the relationship between code blocks, specifically the namespace, class method level, and the nature of nested code blocks. Nested code serves a purpose, but deeply nested code should be avoided as much as possible to ensure readability. Whenever possible, simplify your code to help yourself and others when reading it. Upcoming lessons will detail different ways to simplify your code without sacrificing functionality.


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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