Variables in .NET

Variables are fundamental to programming. They are named storage locations that hold values. In .NET, you declare a variable by specifying its type and a name, and optionally initializing it with a value.

Declaring and Initializing Variables

The basic syntax for declaring a variable is:

<data_type> <variable_name>;

And to initialize it:

<data_type> <variable_name> = <value>;

int age;
age = 30;

string name = "Alice";

double price = 19.99;

bool isStudent = true;

Variable Naming Rules

• Variable names must start with a letter or an underscore (_).
• They cannot start with a number.
• They can contain letters, numbers, and the underscore character.
• Variable names are case-sensitive (e.g., myVariable is different from myvariable).
• They cannot be C# keywords (like int, string, if, etc.).
• It's a common convention to use camelCase for local variables (e.g., userName) and PascalCase for class members and public properties.

Implicitly Typed Local Variables (var)

C# also supports implicitly typed local variables using the var keyword. The compiler infers the data type from the initialization value.

var count = 100;       // Compiler infers 'int'
var message = "Hello, World!"; // Compiler infers 'string'
var pi = 3.14159;      // Compiler infers 'double'

The var keyword can only be used for local variables. The type is determined at compile time, not runtime.

Variable Scope

The scope of a variable refers to the region of your code where it is accessible. Variables declared within a block of code (e.g., inside a method or a loop) are only accessible within that block.

public void MyMethod()
{
    int localVar = 10; // localVar is only accessible within MyMethod
    if (localVar > 5)
    {
        int anotherVar = 20; // anotherVar is only accessible within this if block
        Console.WriteLine(localVar);
        Console.WriteLine(anotherVar);
    }
    // Console.WriteLine(anotherVar); // This would cause a compile-time error
}