Advertisement

---

Top

< Prev

Next >

• Variables in C#


A variable is a value that may change during the execution of a program. This value is stored in a memory location, which can be accessed by its name, which can be referred to as identifier or a variable name.

C# language has specified some rules which should be followed in order to give a variable name in a C# program. These rules are as follows :


• The first character of a variable name must only be either an alphabet or an underscore.
• After, the first character, a variable name may even contain digits.
• A variable name must not contain a space or a comma.
• The total length of a valid variable name could be between 1 and 511 characters.
• C# is a case-sensitive language, hence the variable name total and Total are treated as two different variable names.






Declaring and initializing variables


Let's see an example of how we can declare and initialize variables in a program :



//C# Example of variables 

using System;

class A
{
public static void Main(String[] ar)
{
	//Declaring and initializing local variables
	//With valid identifiers/variable names
	int size = 1000;
	float ink_prc = 9.50f;
	double time = 19.965;
	short _dist2 = 20;
	char alpha_1 = 'a';

	
	//Printing value of each variable
	Console.WriteLine("The value in variable size is : " + size);
	Console.WriteLine("The value in variable inc_prc is : " + ink_prc);
	Console.WriteLine("The value in variable time is : " + time);
	Console.WriteLine("The value in variable _dist2 is : " + _dist2);
	Console.WriteLine("The value in alpha_1 is : " + alpha_1);
}
}





Output




The value in variable size is : 1000
The value in variable inc_prc is : 9.5
The value in variable time is : 19.965
The value in variable dist2 is : 20
The value in alpha_1 is : a








Declaring and initializing multiple variables of the same type


Let's see an example of how we can declare and initialize multiple variables of the same type in just a single line.



//C# Example of variables 
//C# Declaring and initializing multiple variables of the same type, in a single type


using System;

class A
{
public static void Main(String[] ar)
{
	//Declaring and initializing multiple variables of the same type(int), in a single type
	int a = 1000, b, c = 2000;


	//Declaring and initializing multiple variables of same type(float), in a single
	float ink_prc = 9.50f, weight;


	//Declaring and initializing multiple variables of same type(char), in a single
	char ch, alpha_1 = 'a';
}
}



• In the last example we have first declared 3 int type variables, with first variable, a is initialized to the int value 1000, the second variable, b, is left uninitialized and third variable, c, is initialized to the int value 2000.
• Next, we have first declared 2 float type variables, with first variable, ink_prc is initialized to the int value 9.50f, the second variable, weight, is left uninitialized .
• Next, we we have first declared 2 char type variables, with first variable, ch is left uninitialized, while the second variable is initialized to a char value 'a'.


Note: In C#, you cannot use a local variable, unless it is initialized with a value. So, you should initialize an uninitialized variable before you can use it.






• Keywords in C#


Keywords are the special words whose meaning is already defined in C# programming language. These keywords are also known as the reserved words and that's why the name of any keyword cannot be used for a variable name in a C# program. There are about 79 keywords defined in C# language Let's see a table of these keywords defined in C# language.



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








• Contextual Keywords in C#


Besides the above specified regular keywords, C# has also specified 25 contextual keywords. The contextual keywords have a special meaning in a limited program context, and they can be used as an identifier/variable names but only outside that context. Let's see a table of the contextual keywords defined in C# language.



keywords	keywords	keywords	keywords
yield	var	select	partial
join	global	dynamic	sync
when	where	set	partial
let	group	from	alias
await	ascending	descending	get
into	orderby	remove	value
where






Advertisement






• Constants


Constant is a value that remains the same and does not change or it cannot be modified. C# language allows us to define constants in a program, using the keyword const and the value of such constant does not change throughout the course of execution of the program, even when one intentionally tries to modify it. Let's look at an example to define a constant.



//C# Declaring and initializing a constant

using System;

class A
{
public static void Main(String[] ar)
{
	//Declaring a constant with const keyword
	//And initializing it with value 10
	const int distance = 10;

	//Printing the value of a constant
	Console.WriteLine("The value of a constant 'distance' is : " + distance);
}
}





Output




The value of a constant 'distance' is : 10








• you MUST declare and initialize a constant in the same statement


If you want to use a constant value in your program then you MUST declare and initialize a constant in the same statement. Trying to declare and initialize a constant in separate statements, issues a compile error.



//C# You cannot declare and initialize a constant in separate statements.

using System;

class A
{
public static void Main(String[] ar)
{
	//Only declaring a constant with const keyword
	//But we have not initializing it with a value
	const int distance;

	
	//Initializing constant to a value in a different statement
	distance = 30;
}
}





Compile Error




A.cs(11,12): error CS0145: A const field requires a value to be provided



As you can see, the compiler has issued an error stating that the constant declared with const keyword, requires a value to be provided at the time of its declaration and not in a separate statement.






• Trying to modify the a constant value in C++

Let's try to modify a constant value declared with const keyword in a program and see what happens.

//C# Trying to modify value of a constant
//Will issue a compile error

using System;

class A
{
public static void Main(String[] ar)
{
	//Declaring a constant with const keyword
	//And initializing it with value 10
	const int distance = 10;

	//Printing the value of a constant
	Console.WriteLine("The value of constant distance is : " + distance);
	
	//Trying to modify the value of a constant, distance
	distance = 30;
}
}

Output

A.cs(18,2): error CS0131: The left-hand side of an assignment must be a variable, property or indexer

As you can see in the output of the last program, the compiler has thrown an error stating that the left-hand side of an assignment should be either a variable, property or a indexed i.e. it cannot be a constant. So, you cannot modify a constant i.e. once you've declared at a constant using const keyword, its value is just read-only and cannot be modified.

Please share this article -

< Prev

Next >

< C# Variables, Keywords & Constants

If Statement >

Advertisement