โปรแกรมเครื่องคิดเลขอยากทราบ Function เพิ่มเติมหน่อยครับ

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

namespace WindowsFormsCaculator
{
    public partial class Form1 : Form
    {

        //int a;
        bool plus = false;
        bool minus = false;
        bool multiply = false;
        bool divide = false;
        bool power = false;


        public Form1()
        {
            InitializeComponent();
        }


        private void num_0_Click(object sender, EventArgs e)
        {
          textBox1.Text = textBox1.Text + "0";

        }

        private void num_1_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "1";
           
        }

        private void num_2_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "2";
           
        }

        private void num_3_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "3";
           
        }

        private void num_4_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "4";

        }

        private void num_5_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "5";

        }

        private void num_6_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "6";
        }

        private void num_7_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "7";
           
        }

        private void num_8_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "8";
          
        }

        private void num_9_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + "9";
        }

        private void btnBackspace_Click(object sender, EventArgs e)
        {
            int a = textBox1.Text.Length;
            if (textBox1.Text == "")
            {
                textBox1.Text = "";
            }
            else
            {
                textBox1.Text = textBox1.Text.Remove(a - 1);
            }


        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            //if (textBox1.Text == "")
            //    return;
            //textBox1.Text = "";
            textBox1.Clear();
        }

        private void button1_Click(object sender, EventArgs e)
        {
             if  (plus)
            {
                decimal dec = Convert.ToDecimal(textBox1.Tag) + Convert.ToDecimal(textBox1.Text);
                textBox1.Text = dec.ToString();
            }
            else if (minus) 
            {
                decimal dec = Convert.ToDecimal(textBox1.Tag) - Convert.ToDecimal(textBox1.Text);
                textBox1.Text = dec.ToString();
            }
            else if (multiply)
            {
                decimal dec = Convert.ToDecimal(textBox1.Tag) * Convert.ToDecimal(textBox1.Text);
                textBox1.Text = dec.ToString();
            }
            else if (divide)
            {
                if (textBox1.Text == "0")
                {
                    textBox1.Text = "0";
                }
                else if (textBox1.Text != "0")
                {
                    decimal dec = Convert.ToDecimal(textBox1.Tag) / Convert.ToDecimal(textBox1.Text);
                    textBox1.Text = dec.ToString();
                }
            }
            else if (power)
            {
                decimal dec = Convert.ToDecimal(textBox1.Tag) * Convert.ToDecimal(textBox1.Tag);
                textBox1.Text = dec.ToString();
            }

            return ;

        }

        private void btnKoon_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                return;
            }
            else
            {
                multiply = true;
                textBox1.Tag = textBox1.Text;
                textBox1.Text = "";
            }

        }

        private void btnLopp_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                return;
            }
            else
            {
                minus = true;
                textBox1.Tag = textBox1.Text;
                textBox1.Text = "";
            }

        }

        private void btnBuak_Click(object sender, EventArgs e)
        {
           if (textBox1.Text == "")
            {
                return;
              
            }
            else
            {
                plus = true;
                textBox1.Tag = textBox1.Text;
                textBox1.Text = "";
                
            }
        }

        private void btnHan_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                return;
            }
            else
            {
                divide = true;
                textBox1.Tag = textBox1.Text;
                textBox1.Text = "";
            }

        }

        private void btnJud_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.Contains("."))
            {
                return;
            }
            else
            {
                textBox1.Text = textBox1.Text + ".";
            }

        }