using System;

using System.Threading.Tasks;

var account = new Account(0);

​

var tasks = new Task[2];

​

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()}");

​

void Update(Account account)

{

    decimal[] amounts = { 0, 2, -1, 6 };//Total of 7

​

    foreach (var amount in amounts)

    {

        if (amount >= 0)

        {

            account.Credit(amount);

        }

        else

        {

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

        }

    }

}

​

​

​

public class Account

{

    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;

​

        if (balance >= amount)

        {

            balance -= amount;

            appliedAmount = amount;

        }

​

        return appliedAmount;

    }

​

    public void Credit(decimal amount)

    {

        if (amount < 0)

        {

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

        }

​

        balance += amount;

    }

​

    public decimal GetBalance()

    {

        return balance;

    }

​

    public override string? ToString()

    {

        return $"Balance: {GetBalance()}";

    }

}