构造函数

    class Car
    {
        private string description;
        private uint nWheels;
        public Car(string description,uint nWheels)
        {
            this.description = description;
            this.nWheels = nWheels;
        }
        public Car(string description) : this(description, 4)
        {

        }
    }

public static class MoneyExtension
{
    public static void AddToAmount(this MoneyExtension money,decimal amountToAdd)
    {
        money.Amount += amountToAdd;
    }
}