C#

using(MyDerivedXmlTextReader _mdXml = new MyDerivedXmlTextReader(...))<br />
{...}<br />

 _balance += _amount + (amount * 0.1);

Error:
Error	1	Operator '*' cannot be applied to operands of type 'decimal' and 'double'	

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Code:
using System;
using System.Collections.Generic;
using System.Text;
using Wrox.Interfaces;
using Wrox.Classes;

namespace Wrox.Interfaces 
{ public interface IBankAccount 
    { 
        void PayIn(decimal amount); 
        bool Withdraw(decimal amount); 
        decimal Balance 
            { get;} 
    } 
}

namespace Wrox.Classes
{
    public class VenusBankAccount : IBankAccount
    {
        public Exception InsufficientFunds;
        private decimal _balance;
                public void PayIn (decimal _amount) {
            _balance += _amount;
        }
        public bool Withdraw (decimal _amount) {
            if (_balance > _amount)
            { 
                _balance -= _amount;
                return true;
            }
            else
            { 
                throw InsufficientFunds;
            }
        }
        public decimal Balance {
            get
            {
                return _balance;
            }
        }

        public void PayInWithCommission (decimal _amount) {
            //Business rule: This method includes a 10% commission with the payin amount.
            _balance += _amount + (amount * 0.1);
        }
    }
}
namespace TestConsole
{

    class Program
    {
        static void Main(string[] args)
        {
            IBankAccount myFirstBankAccount = new VenusBankAccount();
            myFirstBankAccount.PayIn(1000);

            /* The following line will not execute because the myFirstBankAccount references IBankAccount,
               hence can implement properties and methods defined by IBankAccount interface.                */
            // myFirstBankAccount.PayInWithCommission;

            VenusBankAccount myRealVenusBankAccount = new VenusBankAccount();
            myRealVenusBankAccount.PayInWithCommission(1000);
        }
    }
}