![C#
3. PROGRAM STRUCTURE
Before we study basic building blocks of the C# programming language, let us look
at a bare minimum C# program structure so that we can take it as a reference in
upcoming chapters.
CreatingHelloWorldProgram
A C# program consists of the following parts:
Namespace declaration
A class
Class methods
Class attributes
A Main method
Statements and Expressions
Comments
Let us look at a simple code that prints the words "Hello World":
using System;
namespace HelloWorldApplication
{
class HelloWorld
{
static void Main(string[] args)
{
/* my first program in C# */
Console.WriteLine("Hello World");
Console.ReadKey();
}
}
}
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![C#
width = 3.5;
}
public double GetArea()
{
return length * width;
}
public void Display()
{
Console.WriteLine("Length: {0}", length);
Console.WriteLine("Width: {0}", width);
Console.WriteLine("Area: {0}", GetArea());
}
}
class ExecuteRectangle
{
static void Main(string[] args)
{
Rectangle r = new Rectangle();
r.Acceptdetails();
r.Display();
Console.ReadLine();
}
}
}
When the above code is compiled and executed, it produces the following result:
Length: 4.5
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![C#
An identifier is a name used to identify a class, variable, function, or any other user-
defined item. The basic rules for naming classes in C# are as follows:
A name must begin with a letter that could be followed by a sequence of letters,
digits (0 - 9) or underscore. The first character in an identifier cannot be a
digit.
It must not contain any embedded space or symbol such as ? - +! @ # % ^ &
* ( ) [ ] { } . ; : " ' / and . However, an underscore ( _ ) can be used.
It should not be a C# keyword.
C#Keywords
Keywords are reserved words predefined to the C# compiler. These keywords cannot
be used as identifiers. However, if you want to use these keywords as identifiers, you
may prefix the keyword with the @ character.
In C#, some identifiers have special meaning in context of code, such as get and set
are called contextual keywords.
The following table lists the reserved keywords and contextual keywords in C#:
Reserved Keywords
abstract as base
bool break byte case
catch char checked
class const continue decimal
default delegate do
double else enum event
explicit extern false
finally fixed float for
foreach goto if
implicit In
in (generic
modifier)
int
interface internal is
lock long namespace new
null object operator
out
out
(generic
modifier)
override params
private protected public
readonly ref return sbyte
sealed short sizeof
stackalloc static string struct
switch this throw
true try typeof uint
ulong unchecked unsafe
ushort using virtual void
volatile while
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![C#
{
Console.WriteLine("Length: {0}", length);
Console.WriteLine("Width: {0}", width);
Console.WriteLine("Area: {0}", GetArea());
}
}
class ExecuteRectangle
{
static void Main(string[] args)
{
Rectangle r = new Rectangle();
r.Acceptdetails();
r.Display();
Console.ReadLine();
}
}
}
When the above code is compiled and executed, it produces the following result:
Length: 4.5
Width: 3.5
Area: 15.75
Theusing Keyword
The first statement in any C# program is -
using System;
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![C#
Identifiers
An identifier is a name used to identify a class, variable, function, or any other user-
defined item. The basic rules for naming classes in C# are as follows:
A name must begin with a letter that could be followed by a sequence of letters,
digits (0 - 9), or underscore. The first character in an identifier cannot be a
digit.
It must not contain any embedded space or symbol like ? - +! @ # % ^ & *
( ) [ ] { } . ; : " ' / and . However, an underscore ( _ ) can be used.
It should not be a C# keyword.
C#Keywords
Keywords are reserved words predefined to the C# compiler. These keywords cannot
be used as identifiers. However, if you want to use these keywords as identifiers, you
may prefix them with the @ character.
In C#, some identifiers have special meaning in context of code, such as get and set,
these are called contextual keywords.
The following table lists the reserved keywords and contextual keywords in C#:
Reserved Keywords
abstract as base bool break byte case
catch char checked class const continue decimal
default delegate do double else enum event
explicit extern false finally fixed float for
foreach goto if implicit in
in (generic
modifier)
int
interface internal is lock long namespace new
null object operator out
out
(generic
modifier)
override params
private protected public readonly ref return sbyte
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![C#
short 16-bit signed integer type -32,768 to 32,767 0
uint
32-bit unsigned integer
type
0 to 4,294,967,295 0
ulong
64-bit unsigned integer
type
0 to 18,446,744,073,709,551,615 0
ushort
16-bit unsigned integer
type
0 to 65,535 0
To get the exact size of a type or a variable on a particular platform, you can use
the sizeof method. The expression sizeof(type) yields the storage size of the object
or type in bytes. Following is an example to get the size of int type on any machine:
namespace DataTypeApplication
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Size of int: {0}", sizeof(int));
Console.ReadLine();
}
}
}
When the above code is compiled and executed, it produces the following result:
Size of int: 4
ReferenceType
The reference types do not contain the actual data stored in a variable, but they
contain a reference to the variables.
In other words, they refer to a memory location. Using multiple variables, the
reference types can refer to a memory location. If the data in the memory location
is changed by one of the variables, the other variable automatically reflects this
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Csharp tutorial
- 1. C#
- 2. C# AbouttheTutorial C# is a simple, modern, general-purpose, object-oriented programming language developed by Microsoft within its .NET initiative led by Anders Hejlsberg. This tutorial covers basic C# programming and various advanced concepts related to C# programming language. Audience This tutorial has been prepared for the beginners to help them understand basics of c# Programming. Prerequisites C# programming is very much based on C and C++ programming languages, so if you have a basic understanding of C or C++ programming, then it will be fun to learn C#. Disclaimer&Copyright Copyright 2014 by Tutorials Point (I) Pvt. Ltd. All the content and graphics published in this e-book are the property of Tutorials Point (I) Pvt. Ltd. The user of this e-book is prohibited to reuse, retain, copy, distribute or republish any contents or a part of contents of this e-book in any manner without written consent of the publisher. We strive to update the contents of our website and tutorials as timely and as precisely as possible, however, the contents may contain inaccuracies or errors. Tutorials Point (I) Pvt. Ltd. provides no guarantee regarding the accuracy, timeliness or completeness of our website or its contents including this tutorial. If you discover any errors on our website or in this tutorial, please notify us at [email protected]. i
- 3. C# Contents About the Tutorial ......................................................................................................................................i Audience.....................................................................................................................................................i Prerequisites...............................................................................................................................................i Disclaimer & Copyright ...............................................................................................................................i Contents ....................................................................................................................................................ii 1. OVERVIEW............................................................................................................................. 1 Strong Programming Features of C# ..........................................................................................................1 2. ENVIRONMENT...................................................................................................................... 3 The .Net Framework..................................................................................................................................3 Integrated Development Environment (IDE) for C#....................................................................................4 Writing C# Programs on Linux or Mac OS...................................................................................................4 3. PROGRAM STRUCTURE.......................................................................................................... 5 Creating Hello World Program ...................................................................................................................5 Compiling and Executing the Program .......................................................................................................6 C# Keywords............................................................................................................................................10 4. BASIC SYNTAX...................................................................................................................... 12 The using Keyword .................................................................................................................................. 13 The class Keyword ...................................................................................................................................14 Comments in C#.......................................................................................................................................14 Member Variables ...................................................................................................................................14 Member Functions...................................................................................................................................14 Instantiating a Class................................................................................................................................. 14 Identifiers ................................................................................................................................................15 C# Keywords............................................................................................................................................15 5. DATA TYPES......................................................................................................................... 17 ii
- 4. C# Value Type...............................................................................................................................................17 Reference Type........................................................................................................................................18 Object Type .............................................................................................................................................19 Dynamic Type ..........................................................................................................................................19 String Type...............................................................................................................................................19 Pointer Type ............................................................................................................................................20 6. TYPE CONVERSION .............................................................................................................. 21 C# Type Conversion Methods .................................................................................................................. 22 7. VARIABLES........................................................................................................................... 24 Defining Variables....................................................................................................................................24 Initializing Variables.................................................................................................................................25 Accepting Values from User.....................................................................................................................26 Lvalue and Rvalue Expressions in C#:.......................................................................................................26 8. CONSTANTS AND LITERALS.................................................................................................. 28 Integer Literals.........................................................................................................................................28 Floating-point Literals..............................................................................................................................29 Character Constants.................................................................................................................................29 String Literals...........................................................................................................................................30 Defining Constants...................................................................................................................................31 9. OPERATORS......................................................................................................................... 33 Arithmetic Operators...............................................................................................................................33 Relational Operators................................................................................................................................ 35 Logical Operators.....................................................................................................................................38 Bitwise Operators....................................................................................................................................40 Assignment Operators .............................................................................................................................43 Miscillaneous Operators..........................................................................................................................46 iii
- 5. C# Operator Precedence in C# ......................................................................................................................48 10. DECISION MAKING............................................................................................................... 51 if Statement.............................................................................................................................................52 if...else Statement ...................................................................................................................................54 The if...else if...else Statement.................................................................................................................56 Nested if Statements ...............................................................................................................................58 Switch Statement ....................................................................................................................................60 The ? : Operator.......................................................................................................................................65 11. LOOPS ................................................................................................................................. 66 While Loop ..............................................................................................................................................67 For Loop...................................................................................................................................................69 Do...While Loop .......................................................................................................................................72 Nested Loops...........................................................................................................................................75 Loop Control Statements .........................................................................................................................78 Infinite Loop ............................................................................................................................................83 12. ENCAPSULATION ................................................................................................................. 84 Public Access Specifier .............................................................................................................................84 Private Access Specifier ...........................................................................................................................86 Protected Access Specifier .......................................................................................................................88 Internal Access Specifier ..........................................................................................................................88 13. METHODS............................................................................................................................ 91 Defining Methods in C#............................................................................................................................91 Calling Methods in C# ..............................................................................................................................92 Recursive Method Call .............................................................................................................................95 Passing Parameters to a Method .............................................................................................................96 Passing Parameters by Value ...................................................................................................................97 iv
- 6. C# Passing Parameters by Reference ............................................................................................................99 Passing Parameters by Output............................................................................................................... 100 14. NULLABLES........................................................................................................................ 104 The Null Coalescing Operator (??).......................................................................................................... 105 15. ARRAYS.............................................................................................................................. 107 Declaring Arrays .................................................................................................................................... 107 Initializing an Array................................................................................................................................ 107 Assigning Values to an Array..................................................................................................................108 Accessing Array Elements ...................................................................................................................... 108 Using the foreach Loop .......................................................................................................................... 110 C# Arrays ...............................................................................................................................................111 Multidimensional Arrays ....................................................................................................................... 112 Two-Dimensional Arrays........................................................................................................................ 112 Jagged Arrays......................................................................................................................................... 115 Passing Arrays as Function Arguments................................................................................................... 117 Param Arrays ......................................................................................................................................... 118 Array Class............................................................................................................................................. 119 Properties of the Array Class.................................................................................................................. 119 Methods of the Array Class.................................................................................................................... 120 16. STRINGS............................................................................................................................. 124 Creating a String Object ......................................................................................................................... 124 Properties of the String Class .................................................................................................................126 Methods of the String Class ...................................................................................................................126 17. STRUCTURES ..................................................................................................................... 135 Defining a Structure............................................................................................................................... 135 Features of C# Structures....................................................................................................................... 137 v
- 7. C# Class versus Structure............................................................................................................................ 138 18. ENUMS.............................................................................................................................. 141 Declaring enum Variable........................................................................................................................ 141 19. CLASSES............................................................................................................................. 143 Defining a Class...................................................................................................................................... 143 Member Functions and Encapsulation................................................................................................... 145 C# Constructors ..................................................................................................................................... 148 C# Destructors ....................................................................................................................................... 151 Static Members of a C# Class ................................................................................................................. 152 20. INHERITANCE..................................................................................................................... 156 Base and Derived Classes....................................................................................................................... 156 Initializing Base Class ............................................................................................................................. 158 Multiple Inheritance in C#...................................................................................................................... 160 21. POLYMORPHISM................................................................................................................ 163 Static Polymorphism.............................................................................................................................. 163 Dynamic Polymorphism.........................................................................................................................165 22. OPERATOR OVERLOADING ................................................................................................ 170 Implementing the Operator Overloading............................................................................................... 170 Overloadable and Non-Overloadable Operators.................................................................................... 173 23. INTERFACES....................................................................................................................... 181 Declaring Interfaces............................................................................................................................... 181 24. NAMESPACES .................................................................................................................... 184 Defining a Namespace ...........................................................................................................................184 The using Keyword................................................................................................................................. 185 Nested Namespaces............................................................................................................................... 187 vi
- 8. C# 25. PREPROCESSOR DIRECTIVES.............................................................................................. 190 Preprocessor Directives in C#.................................................................................................................190 The #define Preprocessor ...................................................................................................................... 191 Conditional Directives............................................................................................................................ 192 26. REGULAR EXPRESSIONS..................................................................................................... 194 Constructs for Defining Regular Expressions..........................................................................................194 Character Escapes.................................................................................................................................. 194 Character Classes................................................................................................................................... 196 Grouping Constructs .............................................................................................................................. 198 Quantifier .............................................................................................................................................. 199 Backreference Constructs ...................................................................................................................... 200 Alternation Constructs........................................................................................................................... 201 Substitution...........................................................................................................................................202 Miscellaneous Constructs ...................................................................................................................... 202 The Regex Class ..................................................................................................................................... 203 27. EXCEPTION HANDLING ...................................................................................................... 208 Exception Classes in C# .......................................................................................................................... 209 Handling Exceptions .............................................................................................................................. 210 Creating User-Defined Exceptions.......................................................................................................... 212 Throwing Objects................................................................................................................................... 213 28. FILE I/O.............................................................................................................................. 214 C# I/O Classes ........................................................................................................................................ 214 The FileStream Class .............................................................................................................................. 215 Advanced File Operations in C# .............................................................................................................217 Reading from and Writing to Text Files.................................................................................................. 218 The StreamReader Class ........................................................................................................................ 218 The StreamWriter Class ......................................................................................................................... 220 vii
- 9. C# Reading from and Writing into Binary files ............................................................................................ 222 The BinaryWriter Class........................................................................................................................... 224 Windows File System............................................................................................................................. 228 The DirectoryInfo Class ..........................................................................................................................228 The FileInfo Class ................................................................................................................................... 230 29. ATTRIBUTES....................................................................................................................... 234 Specifying an Attribute ..........................................................................................................................234 Predefined Attributes ............................................................................................................................ 234 AttributeUsage ...................................................................................................................................... 234 Conditional ............................................................................................................................................ 235 Obsolete ................................................................................................................................................ 237 Creating Custom Attributes ................................................................................................................... 238 Constructing the Custom Attribute ........................................................................................................ 239 Applying the Custom Attribute ..............................................................................................................241 30. REFLECTION....................................................................................................................... 243 Applications of Reflection...................................................................................................................... 243 Viewing Metadata ................................................................................................................................. 243 31. PROPERTIES....................................................................................................................... 251 Accessors............................................................................................................................................... 251 Abstract Properties................................................................................................................................ 255 32. INDEXERS .......................................................................................................................... 259 Use of Indexers...................................................................................................................................... 259 Overloaded Indexers.............................................................................................................................. 262 33. DELEGATES........................................................................................................................ 266 Declaring Delegates ............................................................................................................................... 266 Instantiating Delegates.......................................................................................................................... 266 viii
- 10. C# Multicasting of a Delegate ..................................................................................................................... 268 Using Delegates .................................................................................................................................... 270 34. EVENTS.............................................................................................................................. 272 Using Delegates with Events..................................................................................................................272 Declaring Events .................................................................................................................................... 272 35. COLLECTIONS .................................................................................................................... 279 ArrayList Class........................................................................................................................................280 Hashtable Class...................................................................................................................................... 284 SortedList Class...................................................................................................................................... 288 Stack Class .............................................................................................................................................292 Queue Class ........................................................................................................................................... 295 BitArray Class......................................................................................................................................... 297 36. GENERICS .......................................................................................................................... 302 Features of Generics .............................................................................................................................. 304 Generic Methods ................................................................................................................................... 304 Generic Delegates.................................................................................................................................. 306 37. ANONYMOUS METHODS................................................................................................... 309 Writing an Anonymous Method............................................................................................................. 309 38. UNSAFE CODES.................................................................................................................. 312 Pointers ................................................................................................................................................. 312 Retrieving the Data Value Using a Pointer ............................................................................................. 313 Passing Pointers as Parameters to Methods .......................................................................................... 314 Accessing Array Elements Using a Pointer .............................................................................................315 Compiling Unsafe Code.......................................................................................................................... 316 39. MULTITHREADING............................................................................................................. 318 Thread Life Cycle.................................................................................................................................... 318 ix
- 11. C# Properties and Methods of the Thread Class .........................................................................................319 Creating Threads.................................................................................................................................... 323 Managing Threads ................................................................................................................................. 324 Destroying Threads................................................................................................................................ 326 x
- 12. C# 1. OVERVIEW C# is a modern, general-purpose, object-oriented programming language developed by Microsoft and approved by European Computer Manufacturers Association (ECMA) and International Standards Organization (ISO). C# was developed by Anders Hejlsberg and his team during the development of .Net Framework. C# is designed for Common Language Infrastructure (CLI), which consists of the executable code and runtime environment that allows use of various high-level languages on different computer platforms and architectures. The following reasons make C# a widely used professional language: It is a modern, general-purpose programming language It is object oriented. It is component oriented. It is easy to learn. It is a tructured language. It produces efficient programs. It can be compiled on a variety of computer platforms. It is a part of .Net Framework. StrongProgrammingFeaturesofC# Although C# constructs closely follow traditional high-level languages, C and C++ and being an object-oriented programming language. It has strong resemblance with Java, it has numerous strong programming features that make it endearing to a number of programmers worldwide. Following is the list of few important features of C#: Boolean Conditions Automatic Garbage Collection Standard Library Assembly Versioning Properties and Events 1
- 13. C# Delegates and Events Management Easy-to-use Generics Indexers Conditional Compilation Simple Multithreading LINQ and Lambda Expressions Integration with Windows 2
- 14. C# 2. ENVIRONMENT In this chapter, we will discuss the tools required for creating C# programming. We have already mentioned that C# is part of .Net framework and is used for writing .Net applications. Therefore, before discussing the available tools for running a C# program, let us understand how C# relates to the .Net framework. The.NetFramework The .Net framework is a revolutionary platform that helps you to write the following types of applications: Windows applications Web applications Web services The .Net framework applications are multi-platform applications. The framework has been designed in such a way that it can be used from any of the following languages: C#, C++, Visual Basic, Jscript, COBOL, etc. All these languages can access the framework as well as communicate with each other. The .Net framework consists of an enormous library of codes used by the client languages such as C#. Following are some of the components of the .Net framework: Common Language Runtime (CLR) The .Net Framework Class Library Common Language Specification Common Type System Metadata and Assemblies Windows Forms ASP.Net and ASP.Net AJAX ADO.Net Windows Workflow Foundation (WF) Windows Presentation Foundation Windows Communication Foundation (WCF) LINQ For the jobs each of these components perform, please see ASP.Net - Introduction, and for details of each component, please consult Microsoft's documentation. 3
- 15. C# IntegratedDevelopmentEnvironment(IDE)forC# Microsoft provides the following development tools for C# programming: Visual Studio 2010 (VS) Visual C# 2010 Express (VCE) Visual Web Developer The last two are freely available from Microsoft official website. Using these tools, you can write all kinds of C# programs from simple command-line applications to more complex applications. You can also write C# source code files using a basic text editor like Notepad, and compile the code into assemblies using the command-line compiler, which is again a part of the .NET Framework. Visual C# Express and Visual Web Developer Express edition are trimmed down versions of Visual Studio and has the same appearance. They retain most features of Visual Studio. In this tutorial, we have used Visual C# 2010 Express. You can download it from Microsoft Visual Studio. It gets installed automatically on your machine. Note: You need an active internet connection for installing the express edition. WritingC#ProgramsonLinuxorMacOS Although the.NET Framework runs on the Windows operating system, there are some alternative versions that work on other operating systems. Mono is an open-source version of the .NET Framework which includes a C# compiler and runs on several operating systems, including various flavors of Linux and Mac OS. Kindly check Go Mono. The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools for Linux developers. Mono can be run on many operating systems including Android, BSD, iOS, Linux, OS X, Windows, Solaris, and UNIX. 4
- 16. C# 3. PROGRAM STRUCTURE Before we study basic building blocks of the C# programming language, let us look at a bare minimum C# program structure so that we can take it as a reference in upcoming chapters. CreatingHelloWorldProgram A C# program consists of the following parts: Namespace declaration A class Class methods Class attributes A Main method Statements and Expressions Comments Let us look at a simple code that prints the words "Hello World": using System; namespace HelloWorldApplication { class HelloWorld { static void Main(string[] args) { /* my first program in C# */ Console.WriteLine("Hello World"); Console.ReadKey(); } } } 5
- 17. C# When this code is compiled and executed, it produces the following result: Hello World Let us look at the various parts of the given program: The first line of the program using System; - the using keyword is used to include the System namespace in the program. A program generally has multiple using statements. The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld. The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally contain multiple methods. Methods define the behavior of the class. However, the HelloWorld class has only one method Main. The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class does when executed. The next line /*...*/ is ignored by the compiler and it is put to add comments in the program. The Main method specifies its behavior with the statement Console.WriteLine("Hello World"); WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen. The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET. It is worth to note the following points: C# is case sensitive. All statements and expression must end with a semicolon (;). The program execution starts at the Main method. Unlike Java, program file name could be different from the class name. CompilingandExecutingtheProgram If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps: Start Visual Studio. On the menu bar, choose File -> New -> Project. Choose Visual C# from templates, and then choose Windows. Choose Console Application. 6
- 18. C# Specify a name for your project and click OK button. This creates a new project in Solution Explorer. Write code in the Code Editor. Click the Run button or press F5 key to execute the project. A Command Prompt window appears that contains the line Hello World. You can compile a C# program by using the command-line instead of the Visual Studio IDE: Open a text editor and add the above-mentioned code. Save the file as helloworld.cs Open the command prompt tool and go to the directory where you saved the file. Type csc helloworld.cs and press enter to compile your code. If there are no errors in your code, the command prompt takes you to the next line and generates helloworld.exe executable file. Type helloworld to execute your program. You can see the output Hello World printed on the screen. C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or are said to be in the same class. For example, let us consider a Rectangle object. It has attributes such as length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating the area, and displaying details. Let us look at implementation of a Rectangle class and discuss C# basic syntax: using System; namespace RectangleApplication { class Rectangle { // member variables double length; double width; public void Acceptdetails() { length = 4.5; 7
- 19. C# width = 3.5; } public double GetArea() { return length * width; } public void Display() { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } } class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.Acceptdetails(); r.Display(); Console.ReadLine(); } } } When the above code is compiled and executed, it produces the following result: Length: 4.5 8
- 20. C# Width: 3.5 Area: 15.75 The using Keyword The first statement in any C# program is using System; The using keyword is used for including the namespaces in the program. A program can include multiple using statements. The class Keyword The class keyword is used for declaring a class. Comments in C# Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below: /* This program demonstrates The basic syntax of C# programming Language */ Single-line comments are indicated by the '//' symbol. For example, }//end class Rectangle Member Variables Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width. Member Functions Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetails, GetArea and Display. Instantiating a Class In the preceding program, the class ExecuteRectangle contains the Main() method and instantiates the Rectangle class. Identifiers 9
- 21. C# An identifier is a name used to identify a class, variable, function, or any other user- defined item. The basic rules for naming classes in C# are as follows: A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit. It must not contain any embedded space or symbol such as ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and . However, an underscore ( _ ) can be used. It should not be a C# keyword. C#Keywords Keywords are reserved words predefined to the C# compiler. These keywords cannot be used as identifiers. However, if you want to use these keywords as identifiers, you may prefix the keyword with the @ character. In C#, some identifiers have special meaning in context of code, such as get and set are called contextual keywords. The following table lists the reserved keywords and contextual keywords in C#: Reserved Keywords abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit In in (generic modifier) int interface internal is lock long namespace new null object operator out out (generic modifier) override params private protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using virtual void volatile while 10
- 22. C# Contextual Keywords add alias ascending descending dynamic from get global group into join let orderby partial (type) partial (method) remove select set 11
- 23. C# 4. BASIC SYNTAX C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, more often, are said to be in the same class. For example, let us consider an object Rectangle. It has attributes such as length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating area, and display details. Let us look at an implementation of a Rectangle class and discuss C# basic syntax: using System; namespace RectangleApplication { class Rectangle { // member variables double length; double width; public void Acceptdetails() { length = 4.5; width = 3.5; } public double GetArea() { return length * width; } public void Display() 12
- 24. C# { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } } class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.Acceptdetails(); r.Display(); Console.ReadLine(); } } } When the above code is compiled and executed, it produces the following result: Length: 4.5 Width: 3.5 Area: 15.75 Theusing Keyword The first statement in any C# program is - using System; 13
- 25. C# The using keyword is used for including the namespaces in the program. A program can include multiple using statements. TheclassKeyword The class keyword is used for declaring a class. CommentsinC# Comments are used for explaining code. Compiler ignores the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below: /* This program demonstrates The basic syntax of C# programming Language */ Single-line comments are indicated by the '//' symbol. For example, }//end class Rectangle MemberVariables Variables are attributes or data members of a class. They are used for storing data. In the preceding program, the Rectangle class has two member variables named length and width. MemberFunctions Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetails, GetArea, and Display. InstantiatingaClass In the preceding program, the class ExecuteRectangle is used as a class, which contains the Main() method and instantiates the Rectangle class. 14
- 26. C# Identifiers An identifier is a name used to identify a class, variable, function, or any other user- defined item. The basic rules for naming classes in C# are as follows: A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9), or underscore. The first character in an identifier cannot be a digit. It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and . However, an underscore ( _ ) can be used. It should not be a C# keyword. C#Keywords Keywords are reserved words predefined to the C# compiler. These keywords cannot be used as identifiers. However, if you want to use these keywords as identifiers, you may prefix them with the @ character. In C#, some identifiers have special meaning in context of code, such as get and set, these are called contextual keywords. The following table lists the reserved keywords and contextual keywords in C#: Reserved Keywords abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in in (generic modifier) int interface internal is lock long namespace new null object operator out out (generic modifier) override params private protected public readonly ref return sbyte 15
- 27. C# sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using virtual void volatile while Contextual Keywords add alias ascending descending dynamic from get global group into join let orderby partial (type) partial (method) remove select set 16
- 28. C# 5. DATA TYPES The variables in C#, are categorized into the following types: Value types Reference types Pointer types ValueType Value type variables can be assigned a value directly. They are derived from the class System.ValueType. The value types directly contain data. Some examples are int, char, and float, which stores numbers, alphabets, and floating point numbers, respectively. When you declare an int type, the system allocates memory to store the value. The following table lists the available value types in C# 2010: Type Represents Range Default Value bool Boolean value True or False False byte 8-bit unsigned integer 0 to 255 0 char 16-bit Unicode character U +0000 to U +ffff '0' decimal 128-bit precise decimal values with 28-29 significant digits (-7.9 x 1028 to 7.9 x 1028 ) / 100 to 28 0.0M double 64-bit double-precision floating point type (+/-)5.0 x 10-324 to (+/-)1.7 x 10308 0.0D float 32-bit single-precision floating point type -3.4 x 1038 to + 3.4 x 1038 0.0F Int 32-bit signed integer type -2,147,483,648 to 2,147,483,647 0 long 64-bit signed integer type -923,372,036,854,775,808 to 9,223,372,036,854,775,807 0L sbyte 8-bit signed integer type -128 to 127 0 17
- 29. C# short 16-bit signed integer type -32,768 to 32,767 0 uint 32-bit unsigned integer type 0 to 4,294,967,295 0 ulong 64-bit unsigned integer type 0 to 18,446,744,073,709,551,615 0 ushort 16-bit unsigned integer type 0 to 65,535 0 To get the exact size of a type or a variable on a particular platform, you can use the sizeof method. The expression sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine: namespace DataTypeApplication { class Program { static void Main(string[] args) { Console.WriteLine("Size of int: {0}", sizeof(int)); Console.ReadLine(); } } } When the above code is compiled and executed, it produces the following result: Size of int: 4 ReferenceType The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables. In other words, they refer to a memory location. Using multiple variables, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this 18
- 30. C# change in value. Example of built-in reference types are: object, dynamic, and string. ObjectType The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. The object types can be assigned values of any other types, value types, reference types, predefined or user- defined types. However, before assigning values, it needs type conversion. When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing. object obj; obj = 100; // this is boxing DynamicType You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at run-time. Syntax for declaring a dynamic type is: dynamic <variable_name> = value; For example, dynamic d = 20; Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time. StringType The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted. For example, String str = "Tutorials Point"; 19
- 31. C# A @quoted string literal looks as follows: @"Tutorials Point"; The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter. PointerType Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as the pointers in C or C++. Syntax for declaring a pointer type is: type* identifier; For example, char* cptr; int* iptr; We will discuss pointer types in the chapter 'Unsafe Codes'. 20
- 32. C# End of ebook preview If you liked what you saw… Buy it from our store @ https://store.tutorialspoint.com 21