select name in autocomplete text box then load mobile no in 2nd text box

My response to BulletVictim was incorrect. The AutoComplete functionality of the TextBox takes care of the character-by-character input of the user. And BulletVictim is correct in suggesting that you need a Leave event handler.

The solution that I provide is somewhat like the MSDN documentation TextBox.AutoCompleteSource Property [^].

First the code you seek:

//#define SQL

using System;
using System.Data;
using System.Drawing;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace AutoComplete
    {

    // *************************************************** class Form1

    public partial class Form1 : Form
        {

        TextBox     autocomplete_textbox = null;

        // ***************************************************** Form1

        public Form1 ( )
            {
            InitializeComponent ( );

            if ( autocomplete_textbox != null )
                {
                autocomplete_textbox.Dispose ( );
                autocomplete_textbox = null;
                }
            }

        // ******************************* create_autocomplete_textbox

        TextBox create_autocomplete_textbox ( 
                                AutoCompleteStringCollection source )
            {
            TextBox text_box = new TextBox
                              {
                              AutoCompleteCustomSource = source,
                              AutoCompleteMode = 
                                  AutoCompleteMode.SuggestAppend,
                              AutoCompleteSource =
                                  AutoCompleteSource.CustomSource,
                              Location = new Point ( 20, 20 ),
                              Width = ( ClientRectangle.Width - 40 ),
                              Visible = true
                              };
            return ( text_box );
            }
#if SQL
        // ************************************************ Form1_Load

        private void Form1_Load ( object    sender, 
                                  EventArgs e )
            {
            AutoCompleteStringCollection    names;
            string                          command_text;
            string                          connection_string;
            DataTable                       data_table;
            SqlCommand                      sql_command;
            SqlConnection                   sql_connention;
            SqlDataAdapter                  sql_data_adapter;


            connection_string = @"Database Source.....";
            sql_connention = new SqlConnection ( connection_string );
            sql_connention.Open ( );
            command_text = "select * from table1";
            sql_command = new SqlCommand ( command_text,
                                           sql_connention );
            sql_data_adapter = new SqlDataAdapter ( sql_command );
            data_table = new DataTable ( );
            sql_data_adapter.Fill ( data_table );
                                        // names are now in data_table

                                        // create the autocomplete 
            names = new AutoCompleteStringCollection ( );
            foreach ( DataRow data_row in data_table.Rows )
                {
                names.Add ( data_row [ "name" ].ToString ( ) );
                }
                                        // create the textbox
            autocomplete_textbox = create_autocomplete_textbox ( 
                                                          names );
            autocomplete_textbox.Leave += 
                new EventHandler ( 
                    autocomplete_textbox_Leave );

            this.Controls.Add ( autocomplete_textbox );
            }
#else
        // ************************************************ Form1_Load

        // http://msdn.microsoft.com/en-us/library/
        //     system.windows.forms.textbox.
        //     autocompletesource(v=vs.90).aspx

        private void Form1_Load ( object sender,
                                  EventArgs e )
            {
                                        // Create the list to use as 
                                        // the custom source. 
            var months = new AutoCompleteStringCollection ( );
            months.AddRange ( new string [ ] { "January",
                                               "February",
                                               "March",
                                               "April",
                                               "May",
                                               "June",
                                               "July",
                                               "August",
                                               "September",
                                               "October",
                                               "November",
                                               "December"
                                               } );
                                        // initialize the text box
            autocomplete_textbox = create_autocomplete_textbox ( 
                                                            months );
            autocomplete_textbox.Leave += 
                new EventHandler ( 
                    autocomplete_textbox_Leave );

            this.Controls.Add ( autocomplete_textbox );
            }
#endif
        // ******************************** autocomplete_textbox_Leave

        // remember that this event handler is invoked only when there 
        // is more than one control on the form

        void autocomplete_textbox_Leave ( object    sender, 
                                         EventArgs e )
            {
            string  chosen_name = String.Empty;
            TextBox text_box = ( TextBox ) sender;

            chosen_name = text_box.Text;

            MessageBox.Show ( "Chosen: " + chosen_name );
            }

        // ******************************************** exit_BUT_Click

        private void exit_BUT_Click ( object    sender, 
                                      EventArgs e )
            {

            Application.Exit ( );
            }

        } // class Form1

    } // namespace AutoComplete

There are two Form1_Load event handlers. Only one is compiled depending on whether or not the symbol SQL is defined. I added the directives because I do not know your connection string. If you remove the C# preprocessor directives, make sure that you remove the second Form1_Load event handler.

Leaving the code the way it is, all you need is a Form (Form1) and an exit button (exit_BUT) on your form. Leave room at the top for the autocomplete textbox.

I was surprised that I needed to create the TextBox dynamically. But that was my initial problem.

Hope that helps.