Demo 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace OptionParameters
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("可選引數為空時，輸出如下：");
            Test(1);
            Console.WriteLine("命名實參：只給第二個可選引數賦值");
            Test(2, name: "Bill");

            Console.Read();

        }
        /// <summary>
        /// 可選引數測試
        /// </summary>
        /// <param name="x">必選引數</param>
        /// <param name="y">可選引數</param>
        /// <param name="name">可選引數</param>
        static void Test(int x,int y=0,string name = "Allen")
        {
            Console.WriteLine("x={0},y={1},name={2}", x, y, name);
        }
    }
}