public static implicit operator TargetType(SourceType Identifier)
{
       ...
      return ObjectOfTargetType;
}

class LimitedInt
    {
        const int MaxValue = 100;
        const int MinValue = 0;

        private int _theValue = 0;
        //屬性
        public int TheValue
        {
            get { return _theValue; }
            set
            {
                if (value < MinValue)
                {
                    _theValue = 0;
                }
                else
                {
                    _theValue = value > MaxValue ? MaxValue : value;
                }
            }
        }

        //隱式轉換:將LimitedInt對象轉為整型
        public static implicit operator int(LimitedInt li)
        {
            return li.TheValue;
        }

        //隱式轉換:將整型轉換為LimitedInt對象
        public static implicit operator LimitedInt(int x)
        {
            LimitedInt li = new LimitedInt();
            li.TheValue = x;
            return li;
        }

    }

    class Program
    {
        static void Main(string[] args)
        {
            LimitedInt li = 500; //將500轉換為LimitedInt

            int value = li;  //將LimitedInt轉換為int

            Console.WriteLine("li:{0},value:{1}", li.TheValue, value);

            Console.ReadKey();
        }

//顯示轉換:將LimitedInt對象轉為整型
        public static explicit operator int(LimitedInt li)
        {
            return li.TheValue;
        }

        //顯示轉換:將整型轉換為LimitedInt對象
        public static explicit operator LimitedInt(int x)
        {
            LimitedInt li = new LimitedInt();
            li.TheValue = x;
            return li;
        }

        static void Main(string[] args)
        {
            LimitedInt li = (LimitedInt)500; //將500強制轉換為LimitedInt

            int value = (int)li;  //將LimitedInt強制轉換為int

            Console.WriteLine("li:{0},value:{1}", li.TheValue, value);

            Console.ReadKey();
        }