C# Rekenmachine

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 RekenmachineProject
{
    public partial class Form1 : Form
    {
        //variabelen
        string input;
        string som1 = string.Empty; //Eerste input
        char inputTekens; //Input tekens
        string som2 = string.Empty; //Tweede input
        double result; //Result
        double numb1;
        double numb2;

        //form
        public Form1()
        {
            InitializeComponent();
        }

        //cijfer intoetsen
        private void allButton_Click(object sender, EventArgs e)
        {
            input += (sender as Button).Text;
            textBoxDisplay.Text = input;
        }

        //plus, min, keer, gedeeld door intoetsen
        private void buttonPlus_Click(object sender, EventArgs e)
        {
            inputTekens = '+';
            som1 = input;
            input = string.Empty;
        }

        private void buttonMin_Click(object sender, EventArgs e)
        {
            inputTekens = '-';
            som1 = input;
            input = string.Empty;
        }

        private void buttonKeer_Click(object sender, EventArgs e)
        {
            inputTekens = '*';
            som1 = input;
            input = string.Empty;
        }

        private void buttonDelen_Click(object sender, EventArgs e)
        {
            inputTekens = ':';
            som1 = input;
            input = string.Empty;
        }

        //Oplossing
        private void buttonOplossing_Click(object sender, EventArgs e)
        {
            som2 = input;
            double.TryParse(som1, out numb1);
            double.TryParse(som2, out numb2);

            if (inputTekens == '+')
            {
                result = numb1 + numb2;
                textBoxDisplay.Text = result.ToString();
            }

            if (inputTekens == '-')
            {
                result = numb1 - numb2;
                textBoxDisplay.Text = result.ToString();
            }

            if (inputTekens == '*')
            {
                result = numb1 * numb2;
                textBoxDisplay.Text = result.ToString();
            }

            if (inputTekens == ':')
            {
                result = numb1 / numb2;
                textBoxDisplay.Text = result.ToString();
            }
        }

        //reset knop
        private void buttonReset_Click(object sender, EventArgs e)
        {
            this.textBoxDisplay.Text = "";
            this.input = string.Empty;
            this.som1 = string.Empty;
            this.som2 = string.Empty;
        }

        //exit knop
        private void buttonExit_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}