Random Generator form1

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 WindowsFormsApplication5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
          /*  int[]  numbers = new int[10] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
            char[] letters = new char[26] { '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' };
            for(int i = 0; i < 24; i++)
            {

            }*/
            char[] letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()_-".ToCharArray();
            Random r = new Random();
            string randomString = "";
            var random = new Random();

            // for (int i = 0; i < letters.Length; i++)
            for (int i = 0; i < 24; i++)
            {
                randomString += letters[r.Next(0,74)].ToString();
            }
            textBox1.Text = randomString;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}