C#生成驗證碼之四位隨機數

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 WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            string vc = "";
            Random rNum = new Random();//隨機生成類
            int num1 = rNum.Next(0, 9);//返回指定范圍內的隨機數
            int num2 = rNum.Next(0, 9);
            int num3 = rNum.Next(0, 9);
            int num4 = rNum.Next(0, 9);

            int[] nums = new int[4] { num1, num2, num3, num4 };
            for (int i = 0; i < nums.Length; i++)//循環添加四個隨機生成數
            {
                vc += nums[i].ToString();
            }
            lblVerificationCode.Text = vc;
        }
        private void btnVerification_Click(object sender, EventArgs e)
        {
            if (txtInput.Text != null && txtInput.Text != "")//用戶輸入不為空
            {
                if (txtInput.Text == lblVerificationCode.Text)//判斷用戶輸入與隨機生成的四位數是否相同
                {
                    MessageBox.Show("驗證成功！");
                }
                else
                {
                    MessageBox.Show("驗證失敗！");
                }
            }
            else
            {
                MessageBox.Show("請輸入驗證碼！");
            }
        }

        
    }
}