calculatrice c sharp

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 NewCalc
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int x;
        Boolean add,mul,sous,div = false;


        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button1.Text;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button2.Text;

        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button3.Text;

        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button4.Text;

        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button5.Text;

        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button6.Text;

        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button7.Text;

        }

        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button8.Text;

        }

        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button9.Text;

        }

        private void button10_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + button10.Text;

        }

        private void button12_Click(object sender, EventArgs e)
        {
            x = int.Parse(textBox1.Text);
            textBox1.Clear();
            add = true;


        }

        private void button13_Click(object sender, EventArgs e)
        {
            x = int.Parse(textBox1.Text);
            textBox1.Clear();
            sous = true;
        }

        private void button14_Click(object sender, EventArgs e)
        {
            x = int.Parse(textBox1.Text);
            textBox1.Clear();
            mul = true;
        }

        private void button15_Click(object sender, EventArgs e)
        {
            x = int.Parse(textBox1.Text);
            textBox1.Clear();
            div = true;
        }

        private void button11_Click(object sender, EventArgs e)
        {
            if (add) { textBox1.Text = (int.Parse(textBox1.Text) + x).ToString(); add = false; }
            if (mul) { textBox1.Text = (int.Parse(textBox1.Text) * x).ToString(); mul = false; }
            if (div) { textBox1.Text = (int.Parse(textBox1.Text) / x).ToString(); div = false; }
            if (sous) { textBox1.Text = (int.Parse(textBox1.Text) - x).ToString(); sous = false; }
        }
    }
}