今天回頭學習c# 的基礎，看到屬性的定義，忽然明白一個簡單的道理：欄位定義為Private，不需要class 的外部進行訪問，那麼就可以搞個屬性對private 的欄位進行get，set，

還有一個理由就是這個private 的欄位有時是隻讀取的，不允許外部賦值寫入，那麼就只搞個get 的屬性OK了

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
 
using System.Threading.Tasks;
using System.Windows.Forms;

namespace SampleClass
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Add add=new
 
 Add();
            add.FirstNumber = 9;
            //add.SencondNumber = 6;   //只讀欄位賦值報錯
            int addResult=add.GetAdd();
            //textBox1.Text = addResult.ToString();
            textBox1.Text = add.SencondNumber.ToString();
        }
    }

    public class Add
    {
        private int firsNumber;
        
 
private int sencondNumber=10;
        public Add()
        {
        }

        public int FirstNumber
        {
            get => firsNumber;
            set => firsNumber = value;
        }

        public int SencondNumber
        {
            get => sencondNumber;     //sendcondNumber 欄位只讀
            //set => sencondNumber = value;
        }

        public int GetAdd()
        {
            return firsNumber + sencondNumber;
        }
    }
}