ক্লাসেস এবং অবজেক্টস (Classes & Objects)

// The blueprint
class Dog
{
    // Properties — what a Dog knows about itself
    public string Name { get; set; }
    public string Breed { get; set; }
    public int Age { get; set; }

    // Constructor — how to build a Dog
    public Dog(string name, string breed, int age)
    {
        Name = name;
        Breed = breed;
        Age = age;
    }

    // Method — what a Dog can do
    public string Bark()
    {
        return Age < 2 ? "Yip! Yip!" : "Woof! Woof!";
    }

    public string Introduce()
    {
        return $"I'm {Name}, a {Age}-year-old {Breed}.";
    }
}

// Create objects from the blueprint
var buddy = new Dog("Buddy", "Golden Retriever", 5);
var puppy = new Dog("Tiny", "Chihuahua", 1);

Console.WriteLine(buddy.Introduce());
Console.WriteLine($"Buddy says: {buddy.Bark()}");
Console.WriteLine(puppy.Introduce());
Console.WriteLine($"Tiny says: {puppy.Bark()}");

I'm Buddy, a 5-year-old Golden Retriever.
Buddy says: Woof! Woof!
I'm Tiny, a 1-year-old Chihuahua.
Tiny says: Yip! Yip!

class BankAccount
{
    public string Owner { get; init; }  // set only during creation

    private decimal _balance;  // private backing field

    public decimal Balance
    {
        get => _balance;
        private set  // only this class can set it
        {
            if (value < 0)
                throw new ArgumentException("Balance can't be negative!");
            _balance = value;
        }
    }

    // Computed property — no backing field needed
    public string Status => Balance > 1000 ? "Gold Member" : "Standard";

    public BankAccount(string owner, decimal initialDeposit)
    {
        Owner = owner;
        Balance = initialDeposit;
    }

    public void Deposit(decimal amount)
    {
        Balance += amount;
        Console.WriteLine($"Deposited {amount:C}. New balance: {Balance:C}");
    }

    public void Withdraw(decimal amount)
    {
        if (amount > Balance)
        {
            Console.WriteLine("Insufficient funds!");
            return;
        }
        Balance -= amount;
        Console.WriteLine($"Withdrew {amount:C}. New balance: {Balance:C}");
    }
}

var account = new BankAccount("Laboni", 500);
Console.WriteLine($"Owner: {account.Owner}, Status: {account.Status}");
account.Deposit(700);
Console.WriteLine($"Status: {account.Status}");
account.Withdraw(200);
account.Withdraw(5000);

Owner: Laboni, Status: Standard
Deposited $700.00. New balance: $1,200.00
Status: Gold Member
Withdrew $200.00. New balance: $1,000.00
Insufficient funds!

class Player
{
    // Static — shared by ALL players
    public static int TotalPlayers { get; private set; } = 0;

    // Instance — unique to each player
    public string Name { get; set; }
    public int Score { get; set; }

    public Player(string name)
    {
        Name = name;
        Score = 0;
        TotalPlayers++;  // every new player increments the count
    }

    // Static method
    public static void ShowPlayerCount()
    {
        Console.WriteLine($"Total players in the game: {TotalPlayers}");
    }

    public override string ToString() => $"{Name} (Score: {Score})";
}

var p1 = new Player("Anika");
var p2 = new Player("Rafi");
var p3 = new Player("Sadia");

p1.Score = 100;
p2.Score = 85;

Console.WriteLine(p1);
Console.WriteLine(p2);
Player.ShowPlayerCount();  // called on the CLASS, not an object

Anika (Score: 100)
Bob (Score: 85)
Total players in the game: 3