BankAccount.cs

using System;

namespace FirstTask
{
    class BankAccount
    {
        private readonly int _accountNumber;
        private readonly int _bankCode;
        private decimal _balance;
        private readonly Currency _currency;
        private readonly bool _overdraftEnabled;

        public BankAccount(int accountNumber, int bankCode, decimal balance, Currency currency, bool overdraftEnabled)
        {
            _accountNumber = accountNumber;
            _bankCode = bankCode;
            _balance = balance;
            _currency = currency;
            _overdraftEnabled = overdraftEnabled;
        }

        public void Insert(decimal amount)
        {
            _balance += amount;
        }

        public void Withdraw(decimal amount)
        {
            if (_balance - amount <= 0 && !_overdraftEnabled)
            {
                Console.WriteLine("Ouch, no can dosville, baby doll!");

                return;
            }

            _balance -= amount;
        }

        public void Do(OperationType operationType, decimal amount)
        {
            var method = GetType().GetMethod(operationType.ToString());

            method.Invoke(this, new object[] {amount});
        }

        public void PrintBalance()
        {
            Console.WriteLine("Account number: {0}/{1}", _accountNumber, _bankCode);
            Console.ForegroundColor = _balance >= 0 ? ConsoleColor.Green : ConsoleColor.Red;
            Console.WriteLine("Balance: {0} {1}", _balance, _currency);
            Console.ForegroundColor = ConsoleColor.White;
        }

        internal enum Currency
        {
             CZK, USD, EUR, ZAR
        }

        internal enum OperationType
        {
            Insert, Withdraw
        }
    }
}

Program.cs

using System;

namespace FirstTask
{
    class Program
    {
        static void Main()
        {
            var firstBankAccount = new BankAccount(123456, 789, 100, BankAccount.Currency.CZK, false);
            var secondBankAccount = new BankAccount(654321, 987, 1000, BankAccount.Currency.ZAR, true);

            SetUpConsole();

            firstBankAccount.Do(BankAccount.OperationType.Insert, 100);
            firstBankAccount.Do(BankAccount.OperationType.Withdraw, 250);
            firstBankAccount.PrintBalance();

            secondBankAccount.Do(BankAccount.OperationType.Withdraw, 10000);
            secondBankAccount.PrintBalance();

            Console.ReadLine();
        }

        private static void SetUpConsole()
        {
            Console.ForegroundColor = ConsoleColor.White;
        }
    }
}