What is the scope of variables in C#

The scope of a variable refers to the part of the program where the variable is accessible. In C#, variables can have different scopes depending on where they are declared.

Local Variables

Local variables are declared within a method and are only accessible within that method. Their lifecycle begins when the method is invoked and ends when the method finishes.

public void ExampleMethod()
{
    int number = 10; // Local variable, only exists in this method
    
    Console.WriteLine(number); // ✔️ you can use it here
}

number = 5; // ❌ this would give an error, it doesn't exist here

Instance Variables

Instance variables (also called fields), are declared within a class but outside of any method. They are accessible by all methods of the class and their lifecycle is the same as that of the class instance.

public class Person
{
    public string name; // Instance variable

    public void ShowName()
    {
        Console.WriteLine(name);  // ✔️ you can use it here
    }
}

name = "Luis"; // ❌ this would give an error, name doesn't exist here

Person person = new Person();
person.name = "Luis"; // ✔️ this works

Static Variables

Static variables are declared with the static keyword and belong to the class (instead of to a specific instance). They are accessible without creating an instance of the class and their lifecycle lasts until the application ends.

public class Counter
{
    public static int GlobalCounter; // Static variable

    public void Increment()
    {
        GlobalCounter++;  // ✔️ you can use it here
    }
}

GlobalCounter = 10;  // ❌ this would give an error, name doesn't exist here

Counter.GlobalCounter = 10; // ✔️ this works