C# | Variables - GeeksforGeeks

11 Feb, 2022
A typical program uses various values that may change during its execution. For example, a program that performs some operations on the values entered by the user. The values entered by one user may differ from those entered by another user. Hence this makes it necessary to use variables as another user may not use the same values. When a user enters a new value that will be used in the process of operation, can store temporarily in the Random Access Memory of computer and these values in this part of memory vary throughout the execution and hence another term for this came which is known as Variables. So basically, a Variable is a placeholder of the information which can be changed at runtime. And variables allows to Retrieve and Manipulate the stored information.
Syntax:
type variable_name = value; 
or
type variable_names;

Example:
char var = 'h'; // Declaring and Initializing character variable
int a, b, c; // Declaring variables a, b and c of int type

Characteristics of Variables:
name : It must be a valid identifier. In above example, var is a valid identifier.
type : It defines the types of information which is to be stored into the variable. In above example char is a type.
value : It is the actual data which is to be stored in the variable. In above example ‘h’ is the value.
Variable names can contain the letters ‘a-z’ or ’A-Z’ or digits 0-9 as well as the character ‘_’.
The name of the variables cannot be started with a digit.
The name of the variable cannot be any C# keyword say int, float, null, String, etc.
Examples:
Valid Variables Namesint age;

float _studentname;
int age;

float _studentname;
Invalid Variables Namesint if; // "if" is a keyword

float 12studentname; // Cannot start with digit

int if; // "if" is a keyword

float 12studentname; // Cannot start with digit

There are some rules that must be followed while declaring variables :
specify its type (such as int)
specify its name (such as age)
Can provide initial value(such as 17)
Example :
int geeks;
float interest;

The term initializing means to assign some value to the variable. Basically, the actual use of variables comes under the initialization part. In C# each data type has some default value which is used when there is no explicitly set value for a given variable. Initialization can be done separately or may be with declaration.
Example :
int y = 7; // Declaring and initializing the variable at same time
int x; // Declaring variable x
x = 5; // initializing x with value 5
Two Ways for Initialization:
Compile time initializationRun time initialization
Compile time initialization
Run time initialization
It means to provide the value to the variable during the compilation of the program. If the programmer didn’t provide any value then the compiler will provide some default value to the variables in some cases. Generally, this type of initialization helpful when the programmer wants to provide some default value.
Example :
// C# program to demonstrate the // Compile Time Initializationusing System;class Geeks {              // only declaration, compiler will         // provide the default value 0 to it        int y;          // Main Method    public static void Main(String []args)    {                  // Compile Time Initialization of variable 'x'        // Assigning value 32 to x        int x = 32;                      // printing the value        Console.WriteLine("Value of x is "+x);                  // creating object to access        // the variable y        Geeks gfg = new Geeks();                   // printing the value        Console.WriteLine("Value of y is "+gfg.y);    }}
Output :
Value of x is 32
Value of y is 0

In this, the user has to enter the value and that value is copied to the required variable. In this type of initialization, there is one more possibility in which value is assigned to variable after completion of a function call.
Example:
Input : 45
Output : Value of num is 45

Input : 27
Output : Value of num is 27

// C# program to demonstrate the // Run Time Initializationusing System;class Geeks {          // Main Method    public static void Main(String []args)    {                  // Value will be taken from user         // input and assigned to variable        // num        int num = Convert.ToInt32(Console.ReadLine());          // printing the result        Console.WriteLine("Value of num is " + num);      }}
Output :
Value of num is 45

Note: Here the Console.ReadLine() method asks the user to enter the value and later on it puts the same value in the “num” variable. Hence the value will be displayed according to the user input.
shubham_singh
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