首先，刚入门C#可视化，跟老师学习了制作计算器（粗糙版）

用到了Button,Label和TextBox
经测试，正常（包括小数部分）
其中除数为零的处理方式为弹窗显示无穷大，并强制清零
因为测试时发现TextBox显示无穷大后再按符号会出错

以下是代码

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 Calculator
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double i, j, k;
        char a;
        private void button1_Click(object sender, EventArgs e)
        {
            //MessageBox.Show("1");
            textBox1.Text += "1";
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text += "2";
        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text += "3";
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text += "4";
        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text += "5";
        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text += "6";
        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text += "7";
        }

        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text += "8";
        }

        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text += "9";
        }

        private void button0_Click(object sender, EventArgs e)
        {
            textBox1.Text += "0";
        }

        private void point_Click(object sender, EventArgs e)
        {
            textBox1.Text += ".";
        }

        private void equal_Click(object sender, EventArgs e)
        {
            j = Convert.ToDouble(textBox1.Text);
            switch(a)
            {
                case '+':
                    k = i + j;
                    textBox1.Text = k.ToString();
                    break;
                case '-':
                    k = i - j;
                    textBox1.Text = k.ToString();
                    break;
                case '*':
                    k = i * j;
                    textBox1.Text = k.ToString();
                    break;
                case '/':
                    if(i==0)
                    {
                        MessageBox.Show("∞");
                        textBox1.Text = "";
                        break;
                    }
                    k = i / j;
                    textBox1.Text = k.ToString();
                    break;
            }
        }

        private void add_Click(object sender, EventArgs e)
        {
            i = Convert.ToDouble(textBox1.Text);
            textBox1.Text = "";
            a = '+';
        }

        private void subtraction_Click(object sender, EventArgs e)
        {
            i = Convert.ToDouble(textBox1.Text);
            textBox1.Text = "";
            a = '-';
        }

        private void multiplication_Click(object sender, EventArgs e)
        {
            i = Convert.ToDouble(textBox1.Text);
            textBox1.Text = "";
            a = '*';
        }

        private void division_Click(object sender, EventArgs e)
        {
            i = Convert.ToDouble(textBox1.Text);
            textBox1.Text = "";
            a = '/';
        }

        private void clear_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";
        }

        private void fraction_Click(object sender, EventArgs e)
        {
            i = Convert.ToDouble(textBox1.Text);
            if (i == 0)
            {
                MessageBox.Show("∞");
                textBox1.Text = "";
            }
            else
            {
                i = 1 / i;
                textBox1.Text = Convert.ToString(i);
            }
        }
    }
}