GUI password generator

//GUI password generator

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 Password_Generator
{
    public partial class Form1 : Form
    {
        public int numVal;
        public string completed_password;
        public bool includeUpper = false, includerSpecial=false, includeNumbers=false;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            results_textBox1.Text = "";

            Char[] alphabet = new Char[] {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' };
            Int32[] numbers = new Int32[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
            Char[] special = new char[] { '!', '£', '$', '#', '&', '@', '%' };


            try
            {
               numVal= Convert.ToInt32(length_textBox1.Text);
            }
            catch (FormatException ex)
            {
                MessageBox.Show("The length needs to be a NUMBER idiot!");
                length_textBox1.Clear();
            }

            Random rnd = new Random();

            for (int i = 1; i <= numVal; i++)
            {

                //upper?

                if ((i == 2 || i == 5) && includeUpper)
                { completed_password += alphabet[rnd.Next(1, 25)].ToString().ToUpper(); }

                //special?

                else if ((i == 1 || i == 3) && includerSpecial)
                { completed_password += special[rnd.Next(1, 6)].ToString(); }

                //nums?

                else if ((i == 4 || i == 8) && includeNumbers)
                { completed_password += numbers[rnd.Next(1, 9)].ToString(); }


               else { completed_password += alphabet[rnd.Next(1, 25)].ToString(); }

            }

            results_textBox1.Text += completed_password;
            completed_password = "";

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click_1(object sender, EventArgs e)
        {
            Clipboard.SetText(results_textBox1.Text);
            MessageBox.Show("Copied");
        }

        private void upper_checkBox1_Checked(object sender, EventArgs e)
        {
            MessageBox.Show("Blah");
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (upper_checkBox1.Checked) includeUpper = true;
            else includeUpper = false;

            if (special_checkBox1.Checked) includerSpecial = true;
            else includerSpecial = false;

            if (numbers_checkBox1.Checked) includeNumbers = true;
            else includeNumbers = false;



        }
    }
}