Module 3: Using ValueType Variables Contents Overview Common Type System Naming Variables Using Built-in Data Types 14 Creating User-Defined Data Types 22 Converting Data Types 26 Lab 3.1: Creating and Using Types 30 Review 34 Information in this document, including URL and other Internet Web site references, is subject to change without notice Unless otherwise noted, the example companies, organizations, products, domain names, e-mail addresses, logos, people, places, and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, e-mail address, logo, person, places or events is intended or should be inferred Complying with all applicable copyright laws is the responsibility of the user Without limiting the rights under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property  2001−2002 Microsoft Corporation All rights reserved Microsoft, MS-DOS, Windows, Windows NT, ActiveX, BizTalk, IntelliSense, JScript, MSDN, PowerPoint, SQL Server, Visual Basic, Visual C++, Visual C#, Visual J#, Visual Studio, and Win32 are either registered trademarks or trademarks of Microsoft Corporation in the U.S.A and/or other countries The names of actual companies and products mentioned herein may be the trademarks of their respective owners Module 3: Using Value-Type Variables iii Instructor Notes Presentation: 60 Minutes Lab: 35 Minutes This module provides students with an overview of the Common Type System (CTS) Students will learn about value-type variables They will also create and use user-defined data types After completing this module, students will be able to:
Describe the types of variables that can be used in C# applications
Name variables according to standard C# naming conventions
Declare variables by using built-in data types
Assign values to variables
Convert existing variables from one data type to another
Create and use their own data types Materials and Preparation This section provides the materials and preparation tasks that you need to teach this module Required Materials To teach this module, you need the following materials:
Microsoft® PowerPoint® file 2124C_03.ppt
Module 3, “Using Value-Type Variables”
Lab 3, Creating and Using Types Preparation Tasks To prepare for this module, you should:
Read all of the materials for this module
Complete the lab
Read the instructor notes and the margin notes for the module
Read the Naming Guidelines located in the Microsoft NET Framework Software Development Kit (SDK) Help documents
Read the Technical Overview of the Common Language Runtime located in the NET Framework SDK Help documents iv Module 3: Using Value-Type Variables Module Strategy Use the following strategy to present this module:
Common Type System Start this discussion by reminding students that the CTS is a part of the common language runtime (which is covered in Module 1, “Overview of the Microsoft NET Platform,” in Course 2124C, Programming with C# Then discuss the two different categories of types available to programmers in the NET Framework
Naming Variables Start this discussion by reminding students that they must follow the rules and recommendations for C# naming conventions to develop code that functions and is consistent Discuss the naming rules and recommendations for choosing identifiers and reserved keywords
Using Built-in Data Types Explain how to declare local variables and how to handle initially unassigned variables Discuss the assignment operators (=, +=, and so on) Explain compound assignment, increment, and decrement Explain the implicit and explicit conversion Discuss common operators such as equality, relational, conditional, and logical operators Also explain operator precedence and associativity
Creating User-Defined Data Types Explain how to use enum and struct data types and the advantage of the struct data type
Converting Data Types Explain implicit and explicit data type conversions Module 3: Using Value-Type Variables Overview Topic Objective To provide an overview of the module topics and objectives Lead-in In this module, you will learn how to use value-type variables in C#
Common Type System
Naming Variables
Using Built-in Data Types
Creating User-Defined Data Types
Converting Data Types *****************************ILLEGAL FOR NON-TRAINER USE****************************** Delivery Tip For more information about topics mentioned in this module, see the NET Framework class library documentation and the C# Language Specification in the Visual Studio NET Help documents All applications manipulate data in some way As a C# developer, you need to understand how to store and process data in your applications Whenever your application needs to store data temporarily for use during execution, you store that data in a variable Before you use a variable, you must define it When you define a variable, you reserve some storage for that variable by identifying its data type and giving it a name After a variable is defined, you can assign values to that variable In this module, you will learn how to use value-type variables in C# You will learn how to specify the type of data that variables will hold, how to name variables according to standard naming conventions, and how to assign values to variables You also will learn how to convert existing variables from one data type to another and how to create your own variables After completing this module, you will be able to:
Describe the types of variables that you can use in C# applications
Name your variables according to standard C# naming conventions
Declare a variable by using built-in data types
Assign values to variables
Convert existing variables from one data type to another
Create and use your own data types Module 3: Using Value-Type Variables
Common Type System Topic Objective To provide an overview of the topics covered in this section Lead-in In this section, you will learn about some of the data types in C# You will also learn about the Common Type System
Overview of CTS
Comparing Value and Reference Types
Comparing Built-in and User-Defined Value Types
Simple Types *****************************ILLEGAL FOR NON-TRAINER USE****************************** Every variable has a data type that determines what values can be stored in the variable C# is a type-safe language, meaning that the C# compiler guarantees that values stored in variables are always of the appropriate type The common language runtime includes a Common Type System (CTS) that defines a set of built-in data types that you can use to define your variables After completing this lesson, you will be able to:
Describe how the CTS works
Choose the appropriate data types for your variables Module 3: Using Value-Type Variables Overview of CTS Topic Objective To describe CTS Lead-in
CTS supports procedural and object-oriented programming styles The CTS also supports value and reference types CTS supports both value and reference types Type Type Value Value Type Type Reference Reference Type Type *****************************ILLEGAL FOR NON-TRAINER USE****************************** When you define a variable, you need to choose the right data type for your variable The data type determines the allowable values for that variable, which, in turn, determine the operations that can be performed on that variable CTS CTS is an integral part of the common language runtime The compilers, tools, and the runtime itself share CTS It is the model that defines the rules that the runtime follows when declaring, using, and managing types CTS establishes a framework that enables cross-language integration, type safety, and highperformance code execution In this module, you will learn about two types of variables:
Value-type variables
Reference-type variables Module 3: Using Value-Type Variables Comparing Value and Reference Types Topic Objective To describe differences between value and reference types Lead-in The focus of this module is on value types Value types and reference types have significant differences that developers need to understand
Value types:
Reference types:
Directly contain their data
Store references to their data (known as objects)
Each has its own copy of data
Two reference variables can reference same object
Operations on one cannot affect another
Operations on one can affect another *****************************ILLEGAL FOR NON-TRAINER USE****************************** Value Types Value-type variables directly contain their data Each value-type variable has its own copy of the data, so it is not possible for operations on one variable to affect another variable Reference Types Reference-type variables contain references to their data The data for reference-type variables is stored in an object It is possible for two referencetype variables to reference the same object, so it is possible for operations on one reference variable to affect the object referenced by another reference variable Note All of the base data types are defined in the System namespace All types are ultimately derived from System.Object Value types are derived from System.ValueType For more information about reference types, see Module 8, “Using ReferenceType Variables,” in Course 2124C, Programming with C# Module 3: Using Value-Type Variables Comparing Built-in and User-Defined Value Types Topic Objective To compare built-in and user-defined value types Value Types Lead-in Value types include built-in and user-defined types In this topic you will look at some examples of each type Built-in Type
Examples of built-in value types: User-Defined User-Defined
Examples of user-defined value types:
int
enum
float
struct *****************************ILLEGAL FOR NON-TRAINER USE****************************** Value types include built-in and user-defined data types The difference between built-in and user-defined types in C# is minimal because user-defined types can be used in the same way as built-in ones The only real difference between built-in data types and user-defined data types is that you can write literal values for the built-in types All value types directly contain data, and they cannot be null You will learn how to create user-defined data types such as enumeration and structure types in this module Module 3: Using Value-Type Variables Simple Types Topic Objective To describe simple types Lead-in
C# provides a set of predefined struct types called simple types Identified through reserved keywords
int // Reserved keyword - or
System.Int32 *****************************ILLEGAL FOR NON-TRAINER USE****************************** Built-in value types are also referred to as basic data types or simple types Simple types are identified by means of reserved keywords These reserved keywords are aliases for predefined struct types A simple type and the struct type it aliases are completely indistinguishable In your code, you can use the reserved keyword or you can use the struct type The following examples show both: byte // Reserved keyword –Or– System.Byte // struct type int // Reserved keyword –Or– System.Int32 // struct type For more information about the sizes and ranges of built-in value types, search for “Value Types” in the Microsoft® Visual Studio® NET Help documents ... will learn about two types of variables:
Value -type variables
Reference -type variables 4 Module 3: Using Value -Type Variables Comparing Value and Reference Types Topic Objective To describe... variable by using built-in data types
Assign values to variables
Convert existing variables from one data type to another
Create and use your own data types 2 Module 3: Using Value -Type Variables. .. variable by using built-in data types
Use operators to assign values to variables
Define read-only variables and constants Module 3: Using Value -Type Variables 15 Declaring Local Variables