using System;

using System.Threading.Tasks;

public class Account

{

private readonly object balanceLock = new object();

private decimal balance;

public Account(decimal initialBalance) => balance = initialBalance;

public decimal Debit(decimal amount)

{

if (amount < 0)

{

throw new ArgumentOutOfRangeException(nameof(amount), "The debit amount cannot be negative.");

}

decimal appliedAmount = 0;

lock (balanceLock)

{

if (balance >= amount)

{

balance -= amount;

appliedAmount = amount;

Console.WriteLine($"{balance} -= {amount}");

}

}

return appliedAmount;

}

public void Credit(decimal amount)

{

if (amount < 0)

{

throw new ArgumentOutOfRangeException(nameof(amount), "The credit amount cannot be negative.");

}

lock (balanceLock)

{

balance += amount;

Console.WriteLine($"{balance} += {amount}");

}

}

public decimal GetBalance()

{

lock (balanceLock)

{

return balance;

}

}

}

class AccountTest

{

static async Task Main()

{

var account = new Account(1000);

var tasks = new Task[100];

for (int i = 0; i < tasks.Length; i++)

{

tasks[i] = Task.Run(() => Update(account));

}

await Task.WhenAll(tasks);

Console.WriteLine($"Account's balance is {account.GetBalance()}");

// Output:

// Account's balance is 2000

}

static void Update(Account account)

{

decimal[] amounts = { 0, 2, -3, 6, -2, -1, 8, -5, 11, -6 };

foreach (var amount in amounts)

{

if (amount >= 0)

{

account.Credit(amount);

}

else

{

account.Debit(Math.Abs(amount));

}

}

}

}