WinForm : 단순 계산기

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 Winform_01 {
    public partial class Calc : Form {

        //계산기

        public Calc() {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e) {

            string name1 = ((Button)sender).Name;
            string name2 = ((Button)sender).Text;
            int res = 0;

                if (textBox1.Text == string.Empty) {
                    textBox1.Focus();
                    return;
                }
                if (textBox2.Text == string.Empty) {
                    textBox2.Focus();
                    return;
                }
                if (textBox1.Text == string.Empty&& textBox2.Text == string.Empty) {
                    textBox1.Focus();
                    return;
                }
            
                switch (name1) {
                    case "button1":
                        res = int.Parse(textBox1.Text) + int.Parse(textBox2.Text);

                        textBox3.Text = res.ToString();
                        break;
                    case "button2":
                        res = int.Parse(textBox1.Text) - int.Parse(textBox2.Text);

                        textBox3.Text = res.ToString();
                        break;
                    case "button3":
                        res = int.Parse(textBox1.Text) * int.Parse(textBox2.Text);

                        textBox3.Text = res.ToString();
                        break;
                    case "button4":

                        if (int.Parse(textBox2.Text) == 0) {

                            MessageBox.Show("0 으로 나눌수는 없습니다.");
                        }
                        else {
                            res = int.Parse(textBox1.Text) / int.Parse(textBox2.Text);

                            textBox3.Text = res.ToString();
                        }
                        break;
                    case "button5":
                        textBox1.Text = string.Empty;
                        textBox2.Text = string.Empty;
                        textBox3.Text = string.Empty;
                        break;
                }
        }
       }
     }