GUI troubles Optimised

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

namespace DSemulator
{
    public partial class GUI : Form
    {
    Integer screenWidth;
    Integer screenHeight;
    TextBox speedBox;
    TextBox lengthBox;
    TextBox amountBox;
    TextBox faultBox;
    Button startButton;
    ComboBox laneBox;
    Graphics g;

        public GUI(Mainentry mainEntry)
        {
            InitializeComponent();


        //Creating a constant integer for screen width/height prevents repeated calls to
        // Screen.PrimaryScreen.WorkingArea - optimizing the number of calculations done
        screenWidth = Screen.PrimaryScreen.WorkingArea.Width ;
        screenHeight = Screen.PrimaryScreen.WorkingArea.Height;


            g = this.CreateGraphics();

            int X = (screenWidth / 8);
            int Y = (screenHeight / 4) * 3;

            speedBox = new TextBox();
            speedBox.Name = "speedBox";
            speedBox.MaxLength = 5;
            speedBox.Location = new Point(X, Y);
            speedBox.KeyPress += input_KeyPress;

            lengthBox = new TextBox();
            lengthBox.Name = "lengthBox";
            lengthBox.MaxLength = 5;
            lengthBox.Location = new Point(X, Y + 50);
            lengthBox.KeyPress += input_KeyPress;

            amountBox = new TextBox();
            amountBox.Name = "amountBox";
            amountBox.MaxLength = 2;
            amountBox.Location = new Point(X, Y + 100);
            amountBox.KeyPress += amountBox_KeyPress;

            faultBox = new TextBox();
            faultBox.Name = "faultBox";
            faultBox.MaxLength = 2;
            faultBox.Location = new Point(X, Y + 150);
            faultBox.KeyPress += amountBox_KeyPress;

            laneBox = new ComboBox();
            laneBox.Name = "laneBox";
            for (int i = 1; i <= 3; i++)
                laneBox.Items.Add("Drivelane " + i);
            laneBox.SelectedIndex = 0;
            laneBox.Location = new Point(X, Y - 50);

            startButton = new Button();
            startButton.Name = "startButton";
            startButton.Text = "Start";
            startButton.BackColor = Color.Green;
            startButton.Size = new Size(100, 50);
            startButton.Font = new Font("Times New Roman", 20);
            startButton.Location = new Point((screenWidth / 3), (screenHeight / 4) * 3);

            this.Controls.Add(speedBox);
            this.Controls.Add(lengthBox);
            this.Controls.Add(amountBox);
            this.Controls.Add(faultBox);
            this.Controls.Add(laneBox);
            this.Controls.Add(startButton);

            startButton.Click += startButton_Click;
        }

        void startButton_Click(object sender, EventArgs e)
        {
            Control[] temp = this.Controls.Find("speedBox", false);
            float speed = float.Parse(((TextBox)temp[0]).Text);
            ((TextBox)temp[0]).Text = String.Empty;

            temp = this.Controls.Find("lengthBox", false);
            float length = float.Parse(((TextBox)temp[0]).Text);
            ((TextBox)temp[0]).Text = String.Empty;

            temp = this.Controls.Find("amountBox", false);
            int amount = int.Parse(((TextBox)temp[0]).Text);
            ((TextBox)temp[0]).Text = String.Empty;

            temp = this.Controls.Find("faultBox", false);
            int fault = int.Parse(((TextBox)temp[0]).Text);
            ((TextBox)temp[0]).Text = String.Empty;

            temp = this.Controls.Find("laneBox", false);
            int lane = ((ComboBox)temp[0]).SelectedIndex + 1;

            //call some method in another object
        }

        void amountBox_KeyPress(object sender, KeyPressEventArgs e)
        {
            Byte backspace = 0x8;
            if (e.KeyChar >= '0' && e.KeyChar <= '9' || e.KeyChar == Convert.ToChar(backspace))
                e.Handled = false;
            else
                e.Handled = true;
        }

        void input_KeyPress(object sender, KeyPressEventArgs e)
        {
            Byte backspace = 0x8;
            if (e.KeyChar >= '0' && e.KeyChar <= '9' || e.KeyChar == Convert.ToChar(backspace) || e.KeyChar == ',')
                e.Handled = false;  //accept character
            else
                e.Handled = true;   //decline character
        }

         private void GUI_Load(object sender, EventArgs e)
        {
    }
    }
}