C Sharp Syntax Part-1

Let us have a Short  look on  syntax of the C# programming language.

Identifier

An identifier is the name of an element in the code.

An identifier can:

• start with an underscore: _
• contain an underscore: _
• contain a numeral: 0123456789
• contain both upper case and lower case Unicode letters. Case is sensitive (BOX is different from box).

An identifier cannot:

• start with a numeral
• start with a symbol, unless it is a keyword (check Keywords)
• have more than 511 chars
• contain @ sign in between or at the end

Keywords

Keywords are predefined reserved words with special syntactic meaning. 

C# keywords, reserved words abstract as base bool break byte case catch char checked class const continue decimal default delegate do double descending explicit event extern else enum false finally fixed float for foreach from goto group if implicit in int interface internal into is lock long new null namespace object operator out override orderby params private protected public readonly ref return switch struct sbyte sealed short sizeof stackalloc static string select this throw true try typeof uint ulong unchecked unsafe ushort using var virtual volatile void while where

Variables

Variables are identifiers associated with values. They are declared by writing the variable's type and name, and are optionally initialized in the same statement.

Declare

int myInt;         // Declaring an uninitialized variable called 'myInt', of type 'int'

Assigning

int myInt;        // Declaring an uninitialized variable

myInt = 35;       // Assigning the variable a value

Initialize

int myInt = 35;   // Declaring and initializing the variable

Constants

Constants are immutable values. and there value does not change .They are initialized when declared.

const double PI = 3.14;

This shows all the uses of the keyword.

class xyz

{

    const double X = 3;

    xyz()

    {

        const int Y = 2;

    }

}

readonly

The readonly keyword does a similar thing to fields. Like fields marked as const they cannot change once initialized. The difference is that you can choose to initialize them in a constructor. This only works on fields. Read-only fields can either be members of an instance or static class members.

Code blocks

The operators { ... } are used to signify a code block and a new scope. Class members and the body of a method are examples of what can live inside these braces in various contexts.

Inside of method bodies you can use the braces to create new scopes like so:

void doSomething()

{

    int a;

    {

        int b;

        a = 1;

    }

    a = 2;

    b = 3; // Will fail because the variable is declared in an inner scope.

}

Program structure

A C# application consists of classes and their members. Classes and other types exist in namespaces but can also be nested inside other classes.

Main method

 The entry point of the C# application is the Main method. There can only be one, and it is a static method in a class. The method usually returns void and is passed command-line arguments as an array of strings.

static void Main(string[] args)

{

}

// OR Main method can be defined without parameters.

static void Main()

{

}

A Main method is also allowed to return an integer value if specified.

static int Main(string[] args)

{

    return 0;

}

Namespaces

Namespaces are a part of a type name and they are used to group and/or distinguish named entities from other ones.

System.IO.DirectoryInfo // DirectoryInfo is in the System.IO-namespace

A namespace is defined like this:

namespace AAANamespace

{

    // Members

}

Some Commonly used Namespace

Using System; is a statement to indicate that you are using a namespace called System. Basically this namespace contains a class (Console) with methods needed to print the values on the screen and read the values from the keyboard.

Using System.Collections.Generic is a statement to use Generic namespace that contains interfaces and classes to allow the user to create strong types collections.

Using System.Linq; is a statement to use Linq namespace that contains interfaces and classes that support query.

Using System.Text; is a statement to use Text namespace that contains classes that represent ASCII, Unicode, UTF-7, and UTF-8 character encodings, convert bytes to characters and vice versa, and manipulate and format string objects.

For now the last three statements are not important, but they will be used in the next sections of this tutorial.

For the console application, the program will start from Main method of class Program that is contained in a namespace (e.g. Ctest).

Console.WriteLine(“Hello World!”); is used to print the text “Hello World” on the screen.

Console.ReadLine(); is used to read a value from the keyboard.

Operators

Operator category	Operators
Arithmetic	+, -, *, /, %
Logical (boolean and bitwise)	&, |, ^, !, ~, &&, ||, true, false
String concatenation	+
Increment, decrement	++, --
Shift	<<, >>
Relational (conditional)	==, !=, <, >, <=, >=
Assignment	=, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
Member access	.
Indexing	[]
Cast	()
Conditional	?:
Delegate concatenation and removal	+, -
Object creation	new
Type information	as is sizeof typeof
Overflow exception control	checked unchecked
Indirection and Address	*, ->, [], &
Coalesce	??
Lambda expression	=>