基于C#桌面应用制作计算器做出了少量改动，其主要改动为新增加了一个label控件，使其每一步运算结果由label2展示出来，而当点击“=”时，最终运算结果将由label1展示出来，此时label清空。

修改后运行效果

修改后全篇代码

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 WindowsFormsApp计算器
{
    public partial class Form1 : Form
    {
        string symbol, num1, num2,Num1,Num2;
        double rt;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            label1.Text = null;
            label2.Text = null;
            num1=null;
            num2=null;
            symbol = null;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (label1.Text.Length == 0&&symbol==null)
            {
                label1.Text = null;
            }else if (label1.Text.Length == 0 && symbol != null)
            {
                label1.Text = symbol;
            }
            else
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = num1;
                    symbol = null;
                }
                else
                {
                    string del = label1.Text;
                    label1.Text = del.Substring(0, del.Length - 1);
                    label2.Text = label1.Text;
                    if (label2.Text.Length>0&& label1.Text.Length != 0)
                    {
                        num2 = label1.Text;
                        if (symbol == "+")
                        {
                            rt = double.Parse(num1) + double.Parse(num2);
                            label2.Text = rt.ToString();
                        }
                        else if (symbol == "-")
                        {
                            rt = double.Parse(num1) - double.Parse(num2);
                            label2.Text = rt.ToString();
                        }
                        else if (symbol == "×")
                        {
                            rt = double.Parse(num1) * double.Parse(num2);
                            label2.Text = rt.ToString();
                        }
                        else if (symbol == "÷")
                        {
                            rt = double.Parse(num1) / double.Parse(num2);
                            label2.Text = rt.ToString();
                        }
                    }
                    else
                    {
                        if (label1.Text.Length <= 1 && symbol == null)
                        {
                            label2.Text=null;
                        }
                        else
                        {
                            label2.Text = num1;
                        }
                    }
                    if (label1.Text.Length < 30)
                    {
                        if (label1.Text.Length > 16)
                        {
                            label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                        }
                        else
                        {
                            label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                        }
                    }
                }
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
            if (label1.Text.Length == 0)
            {
                MessageBox.Show("error");
            }
            else if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
            {
                MessageBox.Show("error");
            }
            else
            {
                double reserve = double.Parse(label1.Text);
                reserve = -reserve;
                label1.Text = reserve.ToString();
                if (num1 != null && symbol != null)
                {
                    num2 = reserve.ToString();
                    if (symbol == "+")
                    {
                        rt = double.Parse(num1) + double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "-")
                    {
                        rt = double.Parse(num1) - double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "×")
                    {
                        rt = double.Parse(num1) * double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "÷")
                    {
                        rt = double.Parse(num1) / double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                }
            }
        }

        private void button4_Click(object sender, EventArgs e)
        {
            string divide = "÷";
            if (symbol == null && label1.Text.Length<1&&num1==null)
            {
                MessageBox.Show("无运算数字");
            }
            else
            {
                if (symbol == null)
                {
                    if(num1 == null)
                    {
                        num1 = label1.Text;
                    }
                    symbol = divide;
                    label1.Text = symbol;
                    label2.Text = num1;
                }
                else
                {
                        if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷") {
                            MessageBox.Show("您已输入运算符");
                        }
                    else
                    {
                        num2 = label1.Text;
                        num1 = rt.ToString();
                        symbol = divide;
                        label1.Text = symbol;
                        label2.Text = rt.ToString();
                        num2 = null;
                    }
                }
            }
        }

        private void button8_Click(object sender, EventArgs e)
        {
            string seven = "7";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;//如果前面有运算符，则先消除运算符再把数字投射到屏幕上
                }
                label1.Text = label1.Text + seven;//将数字投射到屏幕上
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if(num1!=null&&symbol!=null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button7_Click(object sender, EventArgs e)
        {
            string eight = "8";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + eight;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button6_Click(object sender, EventArgs e)
        {
            string nine = "9";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + nine;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button5_Click(object sender, EventArgs e)
        {
            string multiply = "×";
            if (symbol == null && label1.Text.Length < 1 && num1 == null)
            {
                MessageBox.Show("无运算数字");
            }
            else
            {
                if (symbol == null)
                {
                    if (num1 == null)
                    {
                        num1 = label1.Text;
                    }
                    symbol = multiply;
                    label1.Text = symbol;
                    label2.Text = num1;
                }
                else
                {
                    if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                    {
                        MessageBox.Show("您已输入运算符");
                    }
                    else
                    {
                        num2 = label1.Text;
                        num1 = rt.ToString();
                        symbol = multiply;
                        label1.Text = symbol;
                        label2.Text = rt.ToString();
                        num2 = null;
                    }
                }
            }
        }

        private void button12_Click(object sender, EventArgs e)
        {
            string four = "4";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + four;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button11_Click(object sender, EventArgs e)
        {
            string five = "5";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + five;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button10_Click(object sender, EventArgs e)
        {
            string six = "6";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + six;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button9_Click(object sender, EventArgs e)
        {
            string subtract = "-";
            if (symbol == null && label1.Text.Length < 1 && num1 == null)
            {
                MessageBox.Show("无运算数字");
            }
            else
            {
                if (symbol == null)
                {
                    if (num1 == null)
                    {
                        num1 = label1.Text;
                    }
                    symbol = subtract;
                    label1.Text = symbol;
                    label2.Text = num1;
                }
                else
                {
                    if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                    {
                        MessageBox.Show("您已输入运算符");
                    }
                    else
                    {
                        num2 = label1.Text;
                        num1 = rt.ToString();
                        symbol = subtract;
                        label1.Text = symbol;
                        label2.Text = rt.ToString();
                        num2 = null;
                    }
                }
            }
        }

        private void button16_Click(object sender, EventArgs e)
        {
            string one = "1";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + one;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button15_Click(object sender, EventArgs e)
        {
            string two = "2";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + two;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button14_Click(object sender, EventArgs e)
        {
            string three = "3";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + three;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button13_Click(object sender, EventArgs e)
        {
            string add = "+";
            if (symbol == null && label1.Text.Length < 1 && num1 == null)
            {
                MessageBox.Show("无运算数字");
            }
            else
            {
                if (symbol == null)
                {
                    if (num1 == null)
                    {
                        num1 = label1.Text;
                    }
                    symbol = add;
                    label1.Text = symbol;
                    label2.Text = num1;
                }
                else
                {
                    if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                    {
                        MessageBox.Show("您已输入运算符");
                    }
                    else
                    {
                        num2 = label1.Text;
                        num1 = rt.ToString();
                        symbol = add;
                        label1.Text = symbol;
                        label2.Text = rt.ToString();
                        num2 = null;
                    }
                }
            }
        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void button20_Click(object sender, EventArgs e)
        {
            if (label1.Text.Length == 0)
            {
                MessageBox.Show("error");
            }
            else if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
            {
                MessageBox.Show("error");
            }
            else
            {
                double reserve = double.Parse(label1.Text);
                reserve = reserve / 100;
                label1.Text = reserve.ToString();
                if (num1 != null && symbol != null)
                {
                    num2 = reserve.ToString();
                    if (symbol == "+")
                    {
                        rt = double.Parse(num1) + double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "-")
                    {
                        rt = double.Parse(num1) - double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "×")
                    {
                        rt = double.Parse(num1) * double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                    else if (symbol == "÷")
                    {
                        rt = double.Parse(num1) / double.Parse(num2);
                        label2.Text = rt.ToString();
                    }
                }
            }
        }

        private void button19_Click(object sender, EventArgs e)
        {
            string zero = "0";
            if (label1.Text.Length < 30)
            {
                if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    label1.Text = null;
                }
                label1.Text = label1.Text + zero;
                if (label1.Text.Length > 16)
                {
                    label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                }
                else
                {
                    label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                }
            }
            else
            {
                MessageBox.Show("字符长度超出范围");
            }
            if (num1 != null && symbol != null)
            {
                num2 = label1.Text;
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label2.Text = rt.ToString();
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label2.Text = rt.ToString();
                }
            }
        }

        private void button18_Click(object sender, EventArgs e)
        {
            string dot = ".";
            int f=label1.Text.IndexOf(".");
            if(f == -1)
            {
                if(label1.Text.Length == 0)
                {
                    MessageBox.Show("error");
                }
                else if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                {
                    MessageBox.Show("error");
                }
                else
                {
                    if (label1.Text.Length < 30)
                    {
                        label1.Text = label1.Text + dot;
                        if (label1.Text.Length > 16)
                        {
                            label1.Font = new Font(label1.Font.FontFamily, 13f, label1.Font.Style);
                        }
                        else
                        {
                            label1.Font = new Font(label1.Font.FontFamily, 26f, label1.Font.Style);
                        }
                    }
                    else
                    {
                        MessageBox.Show("字符长度超出范围");
                    }
                }
            }
            else
            {
                MessageBox.Show("error");
            }
        }

        private void button17_Click(object sender, EventArgs e)
        {
            if (symbol == null && label1.Text.Length < 1)
            {
                MessageBox.Show("无运算数字");
            }
            else
            {
                if (symbol == null)
                {
                    num1 = label1.Text;
                }
                else
                {
                    if (label1.Text != null)
                    {
                        if (label1.Text == "+" || label1.Text == "-" || label1.Text == "×" || label1.Text == "÷")
                        {
                            MessageBox.Show("error");
                        }
                        else
                        {
                            num2 = label1.Text;
                        }
                    }
                }
            }
            if (num2 != null)
            {
                if (symbol == "+")
                {
                    rt = double.Parse(num1) + double.Parse(num2);
                    label1.Text = rt.ToString();
                    label2.Text=null;
                    num1 = rt.ToString();
                    symbol = null;
                    num2 = null;
                }
                else if (symbol == "-")
                {
                    rt = double.Parse(num1) - double.Parse(num2);
                    label1.Text = rt.ToString();
                    label2.Text=null;
                    num1 = rt.ToString();
                    symbol = null;
                    num2 = null;
                }
                else if (symbol == "×")
                {
                    rt = double.Parse(num1) * double.Parse(num2);
                    label1.Text = rt.ToString();
                    label2.Text=null;
                    num1 = rt.ToString();
                    symbol = null;
                    num2 = null;
                }
                else if (symbol == "÷")
                {
                    rt = double.Parse(num1) / double.Parse(num2);
                    label1.Text = rt.ToString();
                    label2.Text=null;
                    num1 = rt.ToString();
                    symbol = null;
                    num2 = null;
                }
            }
        }
    }
}