save_txt_file.cs

using System.IO;

namespace TextEditor01
{
    public partial class frmEditor : Form
    {
        public frmEditor()
        {
            InitializeComponent();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            string sText = txtEditor.Text;
            StreamWriter sw = new StreamWriter(@"I:\test\test.txt",true);
            sw.WriteLine(sText);
            sw.Close();

        }
    }
}