What is the difference between shallow copy and deep copy?

Shallow Copy creates a new object but copies only the reference of nested objects. Changes to nested objects affect both the original and copied object.

Deep Copy creates a new object and recursively copies all nested objects. Changes to the copy don't affect the original.

Example:

public class Address
{
    public string Street { get; set; }
    public string City { get; set; }
    
    public Address Clone()
    {
        return new Address
        {
            Street = this.Street,
            City = this.City
        };
    }
}

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Address Address { get; set; }
    
    // Shallow Copy using MemberwiseClone
    public Person ShallowCopy()
    {
        return (Person)this.MemberwiseClone();
    }
    
    // Deep Copy - manually copying all reference types
    public Person DeepCopy()
    {
        return new Person
        {
            Name = this.Name,
            Age = this.Age,
            Address = this.Address?.Clone()  // Clone nested object
        };
    }
}

// Demonstration
class Program
{
    static void Main()
    {
        // Original object
        var person1 = new Person
        {
            Name = "John",
            Age = 30,
            Address = new Address { Street = "123 Main St", City = "New York" }
        };
        
        // Shallow Copy
        var shallowCopy = person1.ShallowCopy();
        shallowCopy.Name = "Jane";  // Changing value type
        shallowCopy.Address.City = "Los Angeles";  // Changing reference type
        
        Console.WriteLine("After Shallow Copy:");
        Console.WriteLine($"Original: {person1.Name}, {person1.Address.City}");
        // Output: Original: John, Los Angeles (City changed!)
        Console.WriteLine($"Shallow Copy: {shallowCopy.Name}, {shallowCopy.Address.City}");
        // Output: Shallow Copy: Jane, Los Angeles
        
        Console.WriteLine();
        
        // Deep Copy
        var person2 = new Person
        {
            Name = "Bob",
            Age = 25,
            Address = new Address { Street = "456 Oak Ave", City = "Chicago" }
        };
        
        var deepCopy = person2.DeepCopy();
        deepCopy.Name = "Alice";
        deepCopy.Address.City = "Boston";
        
        Console.WriteLine("After Deep Copy:");
        Console.WriteLine($"Original: {person2.Name}, {person2.Address.City}");
        // Output: Original: Bob, Chicago (City unchanged!)
        Console.WriteLine($"Deep Copy: {deepCopy.Name}, {deepCopy.Address.City}");
        // Output: Deep Copy: Alice, Boston
    }
}