c# 中属性与字段

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;   //只读字段赋值报错
            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 字段只读
            //set => sencondNumber = value;
        }

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