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HTML / CSS / JS

// Demonstrating value-type vs reference-type copy semantics

// --- Struct (value type) ---
struct Celsius
{
    public double Degrees;
    public Celsius(double d) => Degrees = d;
    public override string ToString() => $"{Degrees}°C";
}

var boiling = new Celsius(100);
var copy    = boiling;         // independent copy
copy.Degrees = 0;
Console.WriteLine(boiling);   // 100°C  — unchanged
Console.WriteLine(copy);      // 0°C

// --- Class (reference type) ---
class Temperature
{
    public double Degrees { get; set; }
    public Temperature(double d) => Degrees = d;
    public override string ToString() => $"{Degrees}°C";
}

var t1 = new Temperature(100);
var t2 = t1;                   // both point to the same object
t2.Degrees = 0;
Console.WriteLine(t1);        // 0°C — mutated via t2!
Console.WriteLine(t2);        // 0°C

// --- String immutability ---
string s1 = "hello";
string s2 = s1;
s2 = s2.ToUpper();            // creates a new string
Console.WriteLine(s1);        // "hello" — unchanged
Console.WriteLine(s2);        // "HELLO"

// --- Span<T> for stack-based slicing (no heap alloc) ---
Span<int> nums = stackalloc int[] { 10, 20, 30, 40 };
var slice = nums[1..3];       // [20, 30]
Console.WriteLine(slice[0]);  // 20