我是刚刚学C#的，老师说要我们设计个计算器，实现加法这步，“为Form1类增加一个变量double sum=0,记录部分和”这个咋弄啊？我不懂在哪添加哦

using System;
using System.Collections.Generic;
using using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace 加法计算器
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double  sum = 0;
           
            double t1 = Convert.ToDouble(textBox1.Text);
            double t2 = Convert.ToDouble(textBox2.Text);
            sum = t1 + t2;
            textBox3.Text = sum.ToString();
        }
    }
}

简单做了个，看看吧，全代码在附件。

非常感谢啊！！！

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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double te1=0, te2=0, sum = 0;
            try
            {
                te1 = Convert.ToDouble(textBox1.Text); //把第一个文本框内的内容转化为第一个数
                te2 = Convert.ToDouble(textBox2.Text); //把第二个文本框内的内容转化为第二个数
                sum = te1 + te2;                       //加法操作
                textBox3.Text = sum.ToString();        //把结果放到第三个文本框
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "tips",MessageBoxButtons.OK, MessageBoxIcon.Warning); //输出出错信息
            }
        }
    }
}