接收返回值问题

Question

那个给详细讲下：using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("请输入你的名字：");
            string name = Convert.ToString(Console.ReadLine());
            Console.Write("{0} :你好！\n请输入你家本月用水量：",name);
            double ysl,feiyong;
            ysl = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("你本月的用水量为：{0}",ysl+"吨");
            //if (ysl <= 3.5)
            //{
            //    ysl = ysl * 2.8;
            //    Console.WriteLine("你应该支付本月水费：{0}", ysl + " 元");
            //}
            //else
            //{
            //    ysl = ysl * 4.2;
            //    Console.WriteLine("你应该支付本月水费：{0}", ysl + " 元");
            //}
            feiyong = shuifei(ys);
            Console.WriteLine("你应该支付本月水费：{0}", feiyong + " 元");
            Console.ReadLine();
        }
        static double shuifei (double ys)
        {
           if(ys <= 3.5)
           {
               return 2.8 * ys;
           }
           else
               return 4.2 * ys;
        }
    }
}

Answer 1

feiyong = shuifei(ys);改为
feiyong = shuifei(ysl);