qr code c# asp.net The C# Language in C#

Generate QR Code in C# The C# Language

The C# Language
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The C# Reserved Keywords
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The C# Contextual Keywords
from join select yield
get let set
global orderby value
Identifiers
In C#, an identifier is a name assigned to a method, a variable, or any other user-defined item Identifiers can be one or more characters long Identifiers may start with any letter of the alphabet or an underscore Next may be a letter, a digit, or an underscore The underscore can be used to enhance the readability of a variable name, as in line_count However, identifers containing two consecutive underscores, such as max_ _value, are reserved for use by the compiler Uppercase and lowercase are different; that is, to C#, myvar and MyVar are separate names Here are some examples of acceptable identifiers:
Test up x _top y2 my_var MaxLoad sample23
2:
An Overview of C#
Remember, you can t start an identifier with a digit Thus, 12x is invalid, for example Good programming practice dictates that you choose identifiers that reflect the meaning or usage of the items being named Although you cannot use any of the reserved C# keywords as identifiers, C# does allow you to precede a keyword with an @, allowing it to be a legal identifier For example, @for is a valid identifier In this case, the identifier is actually for and the @ is ignored Here is a program that illustrates the use of an @ identifier:
// Demonstrate an @ identifier using System; class IdTest { static void Main() { int @if; // use if as an identifier for(@if = 0; @if < 10; @if++) ConsoleWriteLine("@if is " + @if); } }
PART I
The output shown here proves the @if is properly interpreted as an identifier:
@if @if @if @if @if @if @if @if @if @if is is is is is is is is is is 0 1 2 3 4 5 6 7 8 9
Frankly, using @-qualified keywords for identifiers is not recommended, except for special purposes Also, the @ can precede any identifier, but this is considered bad practice
The NET Framework Class Library
The sample programs shown in this chapter make use of two built-in methods: WriteLine( ) and Write( ) As mentioned, these methods are members of the Console class, which is part of the System namespace, which is defined by the NET Framework s class library As explained earlier in this chapter, the C# environment relies on the NET Framework class library to provide support for such things as I/O, string handling, networking, and GUIs Thus, the C# environment as a totality is a combination of the C# language itself, plus the NET standard classes As you will see, the class library provides much of the functionality that is part of any C# program Indeed, part of becoming a C# programmer is learning to use these standard classes Throughout Part I, various elements of the NET library classes and methods are described Part II examines portions of the NET library in detail
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CHAPTER
Data Types, Literals, and Variables
his chapter examines three fundamental elements of C#: data types, literals, and variables In general, the types of data that a language provides define the kinds of problems to which the language can be applied As you might expect, C# offers a rich set of built-in data types, which makes C# suitable for a wide range of applications You can create variables of any of these types, and you can specify constants of each type, which in the language of C# are called literals
Why Data Types Are Important
Data types are especially important in C# because it is a strongly typed language This means that, as a general rule, all operations are type-checked by the compiler for type compatibility Illegal operations will not be compiled Thus, strong type-checking helps prevent errors and enhances reliability To enable strong type-checking, all variables, expressions, and values have a type There is no concept of a typeless variable, for example Furthermore, a value s type determines what operations are allowed on it An operation allowed on one type might not be allowed on another
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