using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;namespace 平方计算器{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void button1_Click(object sender, EventArgs e)        {            double a = double.Parse(textBox1.Text);            double retrun = Math.Sqrt(a);            label1.Text = a + "的平方跟是：" + retrun.ToString() ;//ToString转换字符串。        }        private void Form1_Load(object sender, EventArgs e)        {        }    }}