The Default Keyword in C#

Published: Saturday, May 14, 2022

Updated: Tuesday, May 17, 2022

Greetings, friends! In C#, you can use the default keyword to produce default values for various types. For example, suppose we want to use the default operator to create a default value for the type, int (integer).

csharp

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using System;

public class Program
{
    public static void Main()
    {
        int defaultValue = default(int);
        Console.WriteLine(defaultValue);
        // OUTPUT: 0
    }
}

You can try out this code by copying and pasting it to .NET Fiddle.

By using the default keyword as an operator and passing in a type, we can get the default value for that type. The table shown on Microsoft's default values page lists the default value for each type.

You can also use a default literal to initialize a variable with the default value of its type.

csharp

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using System;

public class Program
{
    public static void Main()
    {
        int defaultValue = default;
        Console.WriteLine(defaultValue);
        // OUTPUT: 0
    }
}

You can even set the parameters of a function to a default literal.

csharp

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using System;

public class Program
{
    public static void Main()
    {
        int someValue = MyFunc();
        Console.WriteLine(someValue);
        // OUTPUT: 3
        
        int someValue2 = MyFunc(4);
        Console.WriteLine(someValue2);
        // OUTPUT: 7
    }

    private static int MyFunc(int a = default)
    {
        // If no value is passed, return 0 + 3 = 3
        return a + 3;
    }
}