Lesson 3: Identifiers, Keywords and Escape Sequence

Identifiers

Identifiers are tokens used to uniquely identify such programming elements as variables, fields, classes, interfaces or methods. In c#, identifiers are case-sensitive and are used whenever we want to reference a particular part of code. C# identifiers are a combination of letters, numbers and underscores.

Keywords

C# identifiers cannot be keywords, reserved words reserved for use by C#. Such special words as class, return, int, and string are typical instances of keywords in c#.

Table below shows the keywords in any part of C# program.

Keyword in C#
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
unit	ulong	unchecked	usafae	ushort
using	virtual	void	volatile	while

C# also has other types of keywords called Contextual Keywords. A contextual keyword is used to provide a specific meaning in the code, but it is not a reserved word in C#; as new keywords are added to the C# language, they are added as contextual keywords in order to avoid breaking programs written in earlier versions.

Contextual keywords in C#
add	alias	ascending
async	await	descending
dynamic	from	get
global	group	into
join	let	orderby
partial ﴾type﴿	partial ﴾method﴿	remove
select	set	value
var	where ﴾generic type constraint﴿	where ﴾query clause﴿
yield

Naming Identifiers

In programming, there are two naming conventions of an identifier – Camel Casting and Pascal Casting.

1. Camel Casting: It is a naming format where the second word in an identifier is begins with a capital letter, it is used mostly with variable names.

Ex. totalRevenue, totalExpense

2. Pascal Casting –a naming convention in which the first letter of the identifier is capitalized; it is used mostly to name methods, classes, namespaces and interfaces.

Ex. GetData(), SetData(), Employee, IEmployee, IO.

In C#, a valid identifier name follows the following rules:

    Rule 1: An identifier must start with a letter or an underscore.
    Rule 2: After the first character, it may contain numbers, letters, connectors, etc
    Rule 3: If the identifier is a keyword, it must be prefixed by @ symbol (at symbol). 

Escape Sequence

Like any c-based languages, C# contains character combinations consisting of a backslash (/) followed by a specific token, and this character combination is called escape sequence. The following table summarizes C# escape sequences.

Escape Sequence
Name	Description
\’	Inserts a single quote in string literal – e.g., Console.Write(“\’single quotes\’);
\”	Inserts a double quote in string literal – e.g., Console.Write(“\”single quotes\”);
\n	Inserts new line
\t	Inserts a horizontal tab into a string literal
\\	Inserts a backslash into a string literal; it can be quite helpful when dealing with a file or network path
\a	Triggers a system alert (beep); and for console applications, it can be an audio clue to the user.

The following program demonstrates the use of escape sequence in C#.

/*

 * Author: Temesghen Tekeste

 * Displaying multiple lines with a single statement.

 * */

using System;

public class EscapeSequenceTest

{

    // C# app begins executing inside the Main method

    public static void Main(string[] args)

    {

        Console.WriteLine("Hello\n there!\n  This\n  is\n"

                            + " escape sequence test in C#");

        Console.WriteLine("Press any key to exit...");

        Console.ReadKey();

    } // end Main

} // end class

Download Source Code

OUTPUT:

References:

 https://msdn.microsoft.com/en-us/library/x53a06bb.aspx

 http://www.infocodify.com/csharp/csharp_identifiers

Lesson 2: Input and Output in C#

Input and Output

WRITE A PROGRAM THAT ASKS A USER WHAT HIS/HER NAME IS AND THEN DISPLAYS THE FOLLOWING TEXT TO THE CONSOLE:

                         Hello, <Name>

Brief Notes: 

• In C#, every code is written inside a class. A class is a blueprint for creating an object; an object is an instance of a class.
• The execution of any C# program starts in a special method called the main method.
• The main method has the following syntax:

                

• To output text to the console we use Write or WritleLine method of the Console class; for example, 
• Console.Write("Enter Your Name:");
• Above code outputs the text Enter Your Name to the console.
• To input data from the console, for instance, name, we first create a variable (a storage location in memory to hold the name) and then we use the ReadLine method of the Console class. For  example: 
• string name = Console.ReadLine();
• Every statement in C# ends in semicolon (;)

Note: We will discuss variables, classes and objects in the coming lessons.

Here is the complete program:

/* 

  * Author: Temesghen Tekeste 

  * email: mail.temesghen.tekeste@gmail.com 

  * */

using System;

namespace ConsoleApplication1

{

    class Program

    {

        static void Main(string[] args)

        {

            Console.Write("What is your name?");

            string name = Console.ReadLine();

            Console.WriteLine();

            Console.WriteLine("Hello, " + name);

            Console.WriteLine("Press any key to exit ...");

            Console.ReadKey();

        }

    }

}

Download Source Code

OUTPUT: