C# - Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C# has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.
We have already discussed various data types. The basic value types provided in C# can be categorized as:

Type	Example
Integral types	sbyte, byte, short, ushort, int, uint, long, ulong and char
Floating point types	float and double
Decimal types	decimal
Boolean types	true or false values, as assigned
Nullable types	Nullable data types

C# also allows defining other value types of variable like enum and reference types of variables like class, which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.

Variable Declaration in C#

Syntax for variable declaration in C# is:

<data_type> <variable_list>;

Here, data_type must be a valid C# data type including char, int, float, double, or any user defined data type etc., and variable_list may consist of one or more identifier names separated by commas.
Some valid variable declarations along with their definition are shown here:

int i, j, k;
char c, ch;
float f, salary;
double d;

You can initialize a variable at the time of declaration as:

int i = 100;

Variable Initialization in C#

Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is:

variable_name = value;

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as:

<data_type> <variable_name> = value;

Some examples are:

int d = 3, f = 5;    /* initializing d and f. */
byte z = 22;         /* initializes z. */
double pi = 3.14159; /* declares an approximation of pi. */
char x = 'x';        /* the variable x has the value 'x'. */

It is a good programming practice to initialize variables properly otherwise, sometime program would produce unexpected result.
Try following example which makes use of various types of variables:

namespace VariableDeclaration
{
    class Program
    {
        static void Main(string[] args)
        {
            short a;
            int b ;
            double c;

            /* actual initialization */
            a = 10;
            b = 20;
            c = a + b;
            Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c);
            Console.ReadLine();
        }
    }
}

When the above code is compiled and executed, it produces following result:

a = 10, b = 20, c = 30

Accepting Values from User

The Console class in the System namespace provides a function ReadLine() for accepting input from the user and store it into a variable. For example,

int num;
num = Convert.ToInt32(Console.ReadLIne());

The function Convert.ToInt32() converts the data entered by the user to int data type, because Console.ReadLine() accepts the data in string format.

Lvalues and Rvalues in C#:

There are two kinds of expressions in C#:

1. lvalue : An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.
2. rvalue : An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement:

int g = 20;

But following is not a valid statement and would generate compile-time error:

10 = 20;

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