Не срабатывает Boolean a; a = true; - C#

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 WindowsFormsApplication15
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
 
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            char kod='0';
            switch (kod)
            {
                /* case kod='+':
                X = Convert.ToInt32(textBox1.Text);
                Y = Convert.ToInt32(textBox1.Text);
                textBox1.text=Convert.ToStr(X+Y);
                       break;
 
                   case kod = '-':
                       break;
                   case kod = '*':
                       break;
                   case kod = '/':
                       break; */
            }
        }
 
        private void button14_Click(object sender, EventArgs e)
        {
            char kod;
            kod = '+';
            int X,Y;
            Boolean a;
            X = Convert.ToInt32(textBox1.Text);
            textBox1.Clear();
            MessageBox.Show("kod");
            Y = Y + Convert.ToInt32(textBox1.Text);
            if (kod=='+') {
                a = false;
            }
            object a = null;
        }
 
        private void button15_Click(object sender, EventArgs e)
        {
            char kod;
            kod = '-';
            var X = Convert.ToInt32(textBox1.Text);
            var Y =Convert.ToInt32(textBox1.Text);
        }
 
        private void button16_Click(object sender, EventArgs e)
        {
            char kod;
            kod = '*';
            var Y = Convert.ToInt32(textBox1.Text);
        }
 
        private void button17_Click(object sender, EventArgs e)
        {
            char kod;
            kod = '/';
            var Y = Convert.ToInt32(textBox1.Text);
        }
 
        private void textBox1_TextChanged(object sender, EventArgs e)
        {
 
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            int X,Y;
            Boolean a;            a = true;
            if(a==true) {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "1";
                    X = Convert.ToInt32(textBox1.Text);
                }
            else
                {
                    textBox1.Clear();
                    textBox1.Text = textBox1.Text + "1";
                    Y = Convert.ToInt32(textBox1.Text)}
                        }
        }
 
        private void button3_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "2";
            }
            bool a;
            a = true;
        }
 
        private void button13_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
        }
 
        private void button12_Click(object sender, EventArgs e)
        {
            int iy,i;
            iy= Convert.ToInt32(textBox1.Text);
            i = iy * iy;
            textBox1.Text = Convert.ToString(i);
        }
 
        private void button4_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "3";
            }
            bool a;
            a = true;
        }
 
        private void button5_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "4";
            }
            bool a;
            a = true;
        }
 
        private void button6_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "5";
            }
            bool a;
            a = true;
        }
 
        private void button7_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "6";
            }
            bool a;
            a = true;
        }
 
        private void button8_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "7";
            }
            bool a;
            a = true;
        }
 
        private void button9_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "8";
            }
            bool a;
            a = true;
        }
 
        private void button10_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "9";
            }
            bool a;
            a = true;
        }
 
        private void button11_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "0")
            {
                textBox1.Clear();
                textBox1.Text = textBox1.Text + "0";
            }
            bool a;
            a = true;
        }
    }
}