How do you give a C# Auto-Property a default value?

In C#, auto-properties provide a shorthand way to declare properties without explicitly writing getter and setter methods. Setting default values for auto-properties can be done in two main ways: using constructor initialization (available in all C# versions) or using property initializers (introduced in C# 6.0).

Syntax

Constructor initialization syntax (C# 5.0 and earlier) −

public class ClassName {
    public PropertyType PropertyName { get; set; }
    
    public ClassName() {
        PropertyName = defaultValue;
    }
}

Property initializer syntax (C# 6.0 and later) −

public class ClassName {
    public PropertyType PropertyName { get; set; } = defaultValue;
}

Using Constructor Initialization

In C# 5.0 and earlier versions, auto-properties could only be initialized in the constructor. The constructor is automatically called when the class is instantiated, setting the property value −

Example

using System;

class Demo {
    public Demo() {
        FirstName = "DemoName";
        Age = 25;
    }
    public string FirstName { get; set; }
    public int Age { get; set; }
}

class Program {
    static void Main() {
        Demo obj = new Demo();
        Console.WriteLine("Name: " + obj.FirstName);
        Console.WriteLine("Age: " + obj.Age);
    }
}

The output of the above code is −

Name: DemoName
Age: 25

Using Property Initializers (C# 6.0+)

C# 6.0 introduced property initializers, allowing you to set default values directly at the property declaration. This approach is more concise and eliminates the need for constructor initialization for simple default values −

Example

using System;

class Demo {
    public string FirstName { get; set; } = "DemoName";
    public int Age { get; set; } = 25;
    public bool IsActive { get; set; } = true;
}

class Program {
    static void Main() {
        Demo obj = new Demo();
        Console.WriteLine("Name: " + obj.FirstName);
        Console.WriteLine("Age: " + obj.Age);
        Console.WriteLine("Active: " + obj.IsActive);
    }
}

The output of the above code is −

Name: DemoName
Age: 25
Active: True

Combining Both Approaches

You can use both property initializers and constructor initialization together. The constructor will override the property initializer values −

Example

using System;

class Demo {
    public string FirstName { get; set; } = "DefaultName";
    public int Age { get; set; } = 18;
    
    public Demo(string name) {
        FirstName = name; // Override the default
    }
}

class Program {
    static void Main() {
        Demo obj1 = new Demo("CustomName");
        Console.WriteLine("Name: " + obj1.FirstName + ", Age: " + obj1.Age);
    }
}

The output of the above code is −

Name: CustomName, Age: 18

Comparison

Conclusion

Auto-properties can be given default values using constructor initialization (all C# versions) or property initializers (C# 6.0+). Property initializers offer cleaner syntax for simple defaults, while constructor initialization provides more flexibility for complex scenarios.