using System;
using System.Collections.Generic;
using System.Windows.Forms;
 
namespace ListBoxOrList
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            var lb = sender as ListBox;
            MessageBox.Show(list[lb.SelectedIndex]);
        }
        List<string> list = new List<string>();
 
        private void Form1_Load(object sender, EventArgs e)
        {
            for (int i = 0; i < 10; i++)
            {
                listBox1.Items.Add(i.ToString());
                list.Add(i.ToString() + "_list");
            }
        }
    }
}