Static variable in C#

Many developers have trouble understanding the functionality of static variables in C#. This article aims to clarify their uses and usage, while explaining why static variables cannot be declared inside methods.

What are static variables?

Static variables are class-level variables that are shared among all instances of that class. Its value is shared among all objects created from the class.

When do I use static variables?

In the case where multiple instances of a class are required to maintain values, static variables are usually used. Some typical use cases include:

• Storage constant value
• Sustain counter
• Share data between different parts of the program

Why can't static variables be declared inside a method?

Static variables are declared outside the method because they have different scopes from instance-level variables. Instance-level variables exist only within the scope of the object instance, while static variables exist in the class itself. Therefore, static variables cannot be declared inside a method because the method has its own isolation scope.

Example:

Consider the following code, which demonstrates the difference between static variables and instance-level variables:

public class Book
{
    public static int myInt = 0; // 静态变量
    public int instanceInt = 5; // 实例级变量
}

public class Exercise
{
    static void Main()
    {
        Book book1 = new Book();
        book1.instanceInt  ; // 增加实例级变量
        book1.myInt  ; // 增加静态变量

        Book book2 = new Book();
        Console.WriteLine(book2.instanceInt); // 输出 5
        Console.WriteLine(book2.myInt); // 输出 1
    }
}

In this example:

• myInt is a static variable that is incremented by 1 every time any object of the Book class is modified.
• instanceInt is an instance-level variable that increments by 1 only to the specific Book object to which it belongs.

in conclusion:

Static variables are powerful tools for storing data shared between multiple instances of a class. Understanding their uses and usage is essential for effective C# programming. However, it is important to remember that static variables cannot be declared inside methods due to different scopes of them.