using System;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string str = null;
            string retString = null;
            str = "This is substring test";
            retString = str.Substring(8, 9);
            MessageBox.Show(retString); 
        }
    }
}