From C#​

var party = new List<Hero> { new Hero("Ada", 30), new Hero("Brom", 22) };
Hero leader = party[0];                      // a second reference to Ada
leader.Hp -= 10;
foreach (var h in party) { h.Hp += 1; }
Hero? target = null;                         // a reference may be empty
target ??= party[1];
Heal(target, 5);
string same = leader == party[0] ? "one Ada" : "two Adas";
Console.WriteLine($"{party[0].Name} {party[0].Hp}, {party[1].Name} {party[1].Hp}, {same}");

static void Heal(Hero hero, int amount) { hero.Hp += amount; }

class Hero {
    public string Name;
    public int Hp;
    public Hero(string name, int hp) { Name = name; Hp = hp; }
}

var units = new List<Unit> { new("ogre", 30), new("imp", 8), new("elf", 15) };
List<string> names = units.Where(u => u.Hp > 10).OrderBy(u => u.Hp).Select(u => u.Name).ToList();
int total = units.Sum(u => u.Hp);
Unit? giant = units.FirstOrDefault(u => u.Hp > 99);
units.Sort((a, b) => b.Hp.CompareTo(a.Hp));  // in place
units.RemoveAll(u => u.Hp < 10);
Console.WriteLine($"{string.Join(", ", names)} | {total} | {giant?.Name ?? "nobody"} | {units[0].Name} of {units.Count}");

record Unit(string Name, int Hp);

var stock = new Dictionary<string, int> { ["arrow"] = 20, ["potion"] = 3 };
stock["rope"] = 1;
stock["arrow"] -= 5;
if (stock.TryGetValue("potion", out int potions)) { Console.WriteLine($"potions: {potions}"); }
int swords = stock.GetValueOrDefault("sword", 0);
try {
    Console.WriteLine(stock["sword"]);
} catch (KeyNotFoundException) {
    Console.WriteLine($"no sword; default {swords}");
}

var counts = new SortedDictionary<string, int>();
foreach (string word in "the cat and the hat".Split(' ')) {
    counts[word] = counts.GetValueOrDefault(word) + 1;
}
var parts = new List<string>();
foreach (var (word, count) in counts) { parts.Add($"{word}={count}"); }
Console.WriteLine(string.Join(" ", parts));

var shapes = new List<Shape> { new Circle(1.0), new Rect(2.0, 3.5) };
double total = 0.0;
foreach (Shape s in shapes) {
    Console.WriteLine(s);
    total += s.Area();
}
Console.WriteLine($"total {total:F2}");

abstract class Shape {
    private readonly string label;
    protected Shape(string label) { this.label = label; }
    public abstract double Area();
    public virtual string Name() => "shape";
    public override string ToString() => $"{label} {Name()}, area {Area():F2}";
}
class Circle : Shape {
    private readonly double radius;
    public Circle(double r) : base("round") { radius = r; }
    public override double Area() => Math.PI * radius * radius;
    public override string Name() => "circle";
}
class Rect : Shape {
    private readonly double width, height;
    public Rect(double w, double h) : base("boxy") { width = w; height = h; }
    public override double Area() => width * height;
}

foreach (int slot in new[] { 1, 7 }) {
    try {
        Save(slot);
    } catch (SaveFailed e) {
        Console.WriteLine($"failed: {e.Message} (slot {e.Slot})");
    }
}

static void Save(int slot) {
    using var guard = new SlotLock(slot);
    if (slot > 3) { throw new SaveFailed(slot, "no such slot"); }
    Console.WriteLine($"saved {slot}");
}

class SaveFailed : Exception {
    public int Slot { get; }
    public SaveFailed(int slot, string why) : base(why) { Slot = slot; }
}
class SlotLock : IDisposable {
    private readonly int slot;
    public SlotLock(int slot) { this.slot = slot; Console.WriteLine($"lock {slot}"); }
    public void Dispose() { Console.WriteLine($"unlock {slot}"); }
}

Paladin p = new Paladin("Ada");
p.Hp = -3;                                   // through the setter
object anyone = p;
object text = "text";
Console.WriteLine($"{p.Describe()} {p.Hp} {Hero.Count} hero: {p}");
Console.WriteLine($"{anyone.GetType().Name == "Hero"} {anyone is Hero} {text is Hero}");

class Hero {
    private int hp = 10;
    public static int Count = 0;
    public string Name;
    public Hero(string name) { Name = name; Count += 1; }
    public int Hp { get => hp; set => hp = value < 0 ? 0 : value; }
    public virtual string Describe() => Name;
    public override string ToString() => $"{Name} ({hp} hp)";
}
class Paladin : Hero {
    public Paladin(string name) : base(name) { }
    public override string Describe() => "Sir " + base.Describe();
}

Sir Ada 0 1 hero: Ada (0 hp)
False True False

var seen = new List<int>();
foreach (int e in Evens(7)) { seen.Add(e); }

var b = new Button();
int clicks = 0;
b.Clicked += () => clicks += 1;
b.Click();
b.Click();

string name = "  Ada ";
name = name.Trim();                          // returns a new string
double hp = 7.25;
int.TryParse("abc", out int parsed);         // false, and parsed is 0
Console.WriteLine($"[{string.Join(",", seen)}] {clicks} {name} has {hp:F1} {int.Parse("42") + 1} {parsed}");

static IEnumerable<int> Evens(int limit) {
    for (int i = 0; i < limit; i += 2) { yield return i; }
}

class Button {
    public event Action? Clicked;
    public void Click() { Clicked?.Invoke(); }
}

Unit a = new Unit();
Unit b = a;                                  // a second reference to one Unit
b.Hp = 50;
Hit(a);
Console.WriteLine($"{a.Hp} {b.Hp}");

var units = new List<Unit> { new Unit(), new Unit() };
foreach (var u in units) { u.Hp -= 5; }      // u refers to the element
Console.WriteLine(units[0].Hp);

static void Hit(Unit u) { u.Hp -= 1; Console.WriteLine($"inside: {u.Hp}"); }   // the caller's Unit

class Unit { public int Hp = 10; }

inside: 49
49 49
5

var units = new List<Unit> { new Unit(), new Unit() };
foreach (var u in units) { u.Hp -= 5; }      // changes the elements
Unit? nobody = null;
Console.WriteLine($"{units[0].Hp} {nobody == null}");

class Unit { public int Hp = 10; }

5 True