在学习之中，希望和大家一起进步

using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
 
namespace WindowsFormsApplication31
{
    public partial class Form1 : Form
    {
        public static double x = 0.0, y = 0.0,s = 0.0,z = 0.0;
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
         
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            x = Convert.ToDouble(textBox1.Text);
            textBox1.Clear();
            textBox1.Focus();
            
            z = 1;
 
        }
 
        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
            textBox1.Focus();
        }
 
        private void button6_Click(object sender, EventArgs e)
        {
            if (z == 1)
            {
                y = Convert.ToDouble(textBox1.Text);
                textBox1.Clear();
                textBox1.Focus();
                s = x + y;
                textBox1.Text = Convert.ToString(s);
            }
            if (z == 2)
            {
                y = Convert.ToDouble(textBox1.Text);
                textBox1.Clear();
                textBox1.Focus();
                s = x - y;
                textBox1.Text = Convert.ToString(s);
            }
            if (z == 3)
            {
                y = Convert.ToDouble(textBox1.Text);
                textBox1.Clear();
                textBox1.Focus();
                s = x * y;
                textBox1.Text = Convert.ToString(s);
            }
            if (z == 4)
            {
                y = Convert.ToDouble(textBox1.Text);
                textBox1.Clear();
                textBox1.Focus();
                s = x / y;
                textBox1.Text = Convert.ToString(s);
            }
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            x = Convert.ToDouble(textBox1.Text);
            textBox1.Clear();
            textBox1.Focus();
            z = 2;
        }
 
        private void button3_Click(object sender, EventArgs e)
        {
            x = Convert.ToDouble(textBox1.Text);
            textBox1.Clear();
            textBox1.Focus();
            z = 3;
        }
 
        private void button4_Click(object sender, EventArgs e)
        {
            x = Convert.ToDouble(textBox1.Text);
            textBox1.Clear();
            textBox1.Focus();
            z = 4;
        }
    }
}
我做的，这个还不够完善，看懂了的话完善很简单。