C#:出题并判断

//出题并判断
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 Test_19
{public partial class Form1 : Form{public Form1(){InitializeComponent();}int a, b;string op;int result;Random rnd = new Random();private void btnJudge_Click(object sender, EventArgs e){string str = txtResult.Text;double d = double.Parse(str);string disp = "" + a + op + b + "=" + str + " ";if (d == result)disp += "√";elsedisp += "×";listJResult.Items.Add(disp);}private void btnNew_Click(object sender, EventArgs e){a = rnd.Next(9) + 1;b = rnd.Next(9) + 1;int c = rnd.Next(4);switch (c){case 0: op = "+";result = a + b;break;case 1: op = "-";result = a - b;break;case 2: op = "*";result = a * b;break;case 3 :op = "/";result = a / b;break;}labOne.Text = a.ToString();labTwo.Text = b.ToString();labFlag.Text = op;txtResult.Text = "";}}
}