Fundamentals of Characters and Strings

Table of contents:

Characters are the fundamental building blocks of C# source code. Every program is composed of characters that, when grouped together meaningfully, create a sequence that the compiler interprets as instructions describing how to accomplish a task. In addition to normal characters, a program also can contain character constants. A character constant is a character that is represented as an integer value, called a character code. For example, the integer value 122 corresponds to the character constant 'z'. The integer value 10 corresponds to the newline character ' '. Character constants are established according to the Unicode character set, an international character set that contains many more symbols and letters than does the ASCII character set (listed in Appendix F). To learn more about Unicode, see Appendix E.

A string is a series of characters treated as a unit. These characters can be uppercase letters, lowercase letters, digits and various special characters: +, -, *, /, $ and others. A string is an object of class string in the System namespace.[1] We write string literals, also called string constants, as sequences of characters in double quotation marks, as follows:

[1] C# provides the string keyword as an alias for class String. In this book, we use the term string.

"John Q. Doe"
"9999 Main Street"
"Waltham, Massachusetts"
"(201) 555-1212"

A declaration can assign a string literal to a string reference. The declaration

string color = "blue";

initializes string reference color to refer to the string literal object "blue".

Performance Tip 16 1

If there are multiple occurrences of the same string literal object in an application, a single copy of the string literal object will be referenced from each location in the program that uses that string literal. It is possible to share the object in this manner, because string literal objects are implicitly constant. Such sharing conserves memory.

On occasion, a string will contain multiple backslash characters (this often occurs in the name of a file). To avoid excessive backslash characters, it is possible to exclude escape sequences and interpret all the characters in a string literally, using the @ character. Backslashes within the double quotation marks following the @ character are not considered escape sequences, but rather regular backslash characters. Often this simplifies programming and makes the code easier to read. For example, consider the string "C:MyFolderMySubFolderMyFile.txt" with the following assignment:

string file = "C:\MyFolder\MySubFolder\MyFile.txt";

Using the verbatim string syntax, the assignment can be altered to

string file = @"C:MyFolderMySubFolderMyFile.txt";

This approach also has the advantage of allowing strings to span multiple lines by preserving all newlines, spaces and tabs.

Preface

Index

    Introduction to Computers, the Internet and Visual C#

    Introduction to the Visual C# 2005 Express Edition IDE

    Introduction to C# Applications

    Introduction to Classes and Objects

    Control Statements: Part 1

    Control Statements: Part 2

    Methods: A Deeper Look

    Arrays

    Classes and Objects: A Deeper Look

    Object-Oriented Programming: Inheritance

    Polymorphism, Interfaces & Operator Overloading

    Exception Handling

    Graphical User Interface Concepts: Part 1

    Graphical User Interface Concepts: Part 2

    Multithreading

    Strings, Characters and Regular Expressions

    Graphics and Multimedia

    Files and Streams

    Extensible Markup Language (XML)

    Database, SQL and ADO.NET

    ASP.NET 2.0, Web Forms and Web Controls

    Web Services

    Networking: Streams-Based Sockets and Datagrams

    Searching and Sorting

    Data Structures

    Generics

    Collections

    Appendix A. Operator Precedence Chart

    Appendix B. Number Systems

    Appendix C. Using the Visual Studio 2005 Debugger

    Appendix D. ASCII Character Set

    Appendix E. Unicode®

    Appendix F. Introduction to XHTML: Part 1

    Appendix G. Introduction to XHTML: Part 2

    Appendix H. HTML/XHTML Special Characters

    Appendix I. HTML/XHTML Colors

    Appendix J. ATM Case Study Code

    Appendix K. UML 2: Additional Diagram Types

    Appendix L. Simple Types

    Index



    Visual C# How to Program
    Visual C# 2005 How to Program (2nd Edition)
    ISBN: 0131525239
    EAN: 2147483647
    Year: 2004
    Pages: 600

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