Now that you can create (and transform) value-based and reference-based variables, you need to examine the

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logical opposite: Constants. C# offers the "const" keyword, to define variables with a fixed, unalterable value.

This comprehensive text starts with a brief overview of the

Unlike C++, the C#C#"const"languagekeywordand thencannotquicklybemovesused toto qualifykey technicalparametersand or return values. Furthermore, it is important to understandarchitecthaturaltheissuesvalueforof.NETa constantdeveloperspoint. of data is computed at compile time, and therefore a constant member cannot be assigned to an object reference (whose value is computed at runtime). Although it is possible to define local constants within a method scope, a more beneficial use of const is to create class-

Table of Contents

level constant definitions. For example:

C# and the .NET Platform, Second Edition

Introduction

// Some const data.

Part One - Introducing C# and the .NET Platform

using System;

Chapter 1 - The Philosophy of .NET

class MyConstants

Chapter 2 - Building C# Applications

{

Part Two - The C# Programming Language

// When accessed by another type, these constants

List of Figurespublic const string myStringConst = "I'm a const";

List of Tables// Don't let the user make this class,

// as its only purpose is to define constant values.

private MyConstants(){ }

}

The same result can be achieved by marking your "constant-only class" as an abstract type. You examine the use of this keyword in the next chapter, but here is the updated MyConstants definition:

// Abstract definition also prevents the creation of a given type.

abstract class MyConstants

{

public const int myIntConst = 5;

public const string myStringConst = "I'm a const";

}

In either case, if another object attempts to create an instance of MyConstants, a compiler error is generated.

C# and the .NET Platform, Second Edition

These techniques can be quite helpful given that C# does not allow you to define global level constants. by Andrew Troelsen ISBN:1590590554

Apress © 2003 (1200 pages)

Referencing Constant Data Across Types

This comprehensive text starts with a brief overview of the

C# language and then quickly moves to key technical and

Given that we havearchitecturalmoved ourissuesconstantfor .NETpointsdevelopersof data into. a new class definition, how are they accessed from within another type? If you attempt to simply reference them by their unqualified name (myIntConstant, myStringConstant) you will be issued a compiler error. Again, the reason has to do with the fact that under C#,

TableglobalofpointsCo tentsof data are not allowed. Thus, any time you wish to access a constant defined outside of the

C#defininga d theclass,.NETyouPlatform,must Secondmake useEditionof the fully-qualified name. On the other hand, if a given class wishes to

Introductionaccess a constant it directly defined, you are able to directly refer to the item at hand:

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

public static void Main()

Chapter 2 - Building C# Applications

{

Part Twoconst- The C#stringP ogramminglocalConstLanguage= "I am a rock, I am an island";

Chapter //3 -UseC# Languageconst dataFundamentals.

Chapter Consol4 - Object.WriteLine("myIntConst-Or ented Programming with C#= {0}\nmyStringConst = {1}\nLocalConst = {2}"

Chapter MyConstants5 - Exceptions.andmyIntConst,Object LifetimeMyConstants.myStringConst, localConst);

}

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

SOURCE The Constants project is located under the Chapter 3 subdirectory.

Chapter 9 - Understanding .NET Assemblies

CODE

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

C# IterationC#Constructsand the .NET Platform, Second Edition

Consider the next few pages a mid-chapter reprieve from the complexities of value/reference types,

Apress © 2003 (1200 pages)

overriding members of System.Object, and boxing types on the heap (in other words, the next few sections

This comprehensive text starts with a brief overview of the

are boring, but necessaryC# languageto cover)and then. Asquicklyyou aremoveswell aware,to key alltechnicalprogrammingand languages provide ways to repeat blocks of codearchitecturuntil alterminatingissues for .NETconditiondevelopershas .been met. Regardless of which language you are coming from, the C# iteration statements should pose no raised eyebrows and require little explanation. In a nutshell, C# provides the following four iteration constructs:

Table of Contents

C#andfortheloop.NET Platform, Second Edition

Introduction

foreach/in loop

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

while loop

Chapter 2 - Building C# Applications

Part Twodo/while- TheloopC# Programming Language

Chapter 3 - C# Language Fundamentals

C, C++, and Java programmers will no doubt be familiar with the "for," "while," and "do/while" loops, but

Chapter 4 - Object-Oriented Programming with C#

may be unfamiliar with the "foreach" statement. Visual Basic programmers on the other hand, are in the fortunate position to be well aware of all four C# iteration statements, as VB already supports "For Each"

syntax. Let's quickly examine each looping construct in turn.

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

The for Loop

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

When you need to iterate over a block of code a fixed number of times, the "for" statement is the construct

Chapter 10 - Processes, AppDomains, Contexts, and Threads

of champions. In essence, you are able to specify how many times a block of code repeats itself, as well as

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

the terminating condition. Without belaboring the point, here is a sample of the syntax:

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

// A basic for loop.

Chapter 13 - Building a Better Window (Introducing Windows Forms) public static int Main(string[] args)

Chapter 14 - A Better Painting Framework (GDI+)

{

Chapter 15 - Programming with Windows Forms Controls

// Note! 'i' is only visible within the scope of the for loop.

Chapter 16 - The System.IO Namespace for(int i = 0; i < 10; i++)

Chapter 17 - Data Access with ADO.NET

{

Part Five - Web Applications and XML Web Services

Console.WriteLine("Number is: {0} ", i);

Chapter 18 - ASP.NET Web Pages and Web Controls

}

Chapter 19 - ASP.NET Web Applications

// 'i' is not visible here.

Chapter 20 - XML Web Services

return 0;

Index}

List of Figures

List of Tables

All of your old C, C++, and Java tricks still hold when building a C# for statement. You can create complex terminating conditions, build endless loops, and make use of the "goto," "continue," and "break" keywords. I'll assume that you will bend this iteration construct as you see fit.

The foreach/in Loop

Visual Basic programmers have long seen the benefits of the For Each construct. The C# equivalent allows you to iterate over all items within an array. Here is a simple example using foreach to traverse an array of strings that represent possible titles for forthcoming publications. Once this array has been filled, you iterate over the contents looking for a pattern match (COM or .NET) using String.IndexOf():

// Digging into an array using foreach.

public static int Main(string[] args)

{

Closely related to the while loop is the do/while statement. Like a simple while loop, do/while is used when

C# and the .NET Platform, Second Edition

you need to perform some action for an undetermined number of times. The difference is that do/while

by Andrew Troelsen ISBN:1590590554

loops are guaranteed to execute the corresponding block of code at least once (in contrast, it is possible

Apress © 2003 (1200 pages)

that a simple while loop may never execute if the terminating condition is false from the onset).

This comprehensive text starts with a brief overview of the

C# language and then quickly moves to key technical and

// The do/while statement

architectural issues for .NET developers.

string ans;

do

Table{ of Contents

Console.Write("Are you done? [yes] [no] : ");

C# and the .NET Platform, Second Edition

ans = Console.ReadLine();

Introduction

}while(ans != "yes");

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

SOURCE The Iterations project is located under the Chapter 3 subdirectory.

Chapter 3 - C# Language Fundamentals

CODE

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

The CompleteC# andSettheof.NETC#Platform,OperatorsSec nd Edition

C# defines a number of operators in addition to those you have previously examined. By and large, these

Apress © 2003 (1200 pages)

operators behave like their C(++) and Java counterparts. Table 3-7 lists the set of C# operators in order of

This comprehensive text starts with a brief overview of the precedence. C# language and then quickly moves to key technical and

architectural issues for .NET developers.

Table 3-7: The Full Set of C# Operators

The only operators that you may not be familiar with are the is and as operators. The is operator is used to

Chapter 17 - Data Access with ADO.NET

verify at runtime if an object is compatible with a given type. One common use for this operator is to

Part Five - Web Applications and XML Web Services

determine if a given object supports a particular interface, as you discover in Chapter 6. The as operator

Chapter 18 - ASP.NET Web Pages and Web Controls

allows you to downcast between types (seen briefly in this chapter and formally in Chapter 4) or

Chapter 19 - ASP.NET Web Applications

implemented interface.

Chapter 20 - XML Web Services

Index

Also note that the C# language does support the use of classic C(++) pointer manipulations, via the *, ->

List of Figures

and & operators. If you choose to make use of these operators, you are bypassing the runtime memory Listmanagementof Tables scheme and writing code in "unsafe mode." You learn about these operators in Chapter 8.

As for the remaining operators, I will make the assumption that many (if not all) of them are old hat to you. If you need additional information regarding the C# looping and decision constructs, consult the C# Language Reference using MSDN.