public Form1()
{
            DateTime dt = DateTime.Now;
            DataTable DTable = new DataTable();
            SqlDataAdapter DAdapter;
            SqlConnection myConnection;
            SqlCommand myCommand;

            InitializeComponent();

            myConnection = new SqlConnection("Server=Server;Trusted_Connection=yes;DataBase=Bar");
            myCommand = new SqlCommand("SELECT КодСотрудника,Фамилия,Имя FROM Сотрудники ORDER BY Фамилия", myConnection);

            try
            {
                DAdapter = new SqlDataAdapter(myCommand);
                DAdapter.Fill(DTable);
            }
            catch (Exception ee)
            {
                Console.WriteLine(ee.ToString());
            }

            textBox1.DataBindings.Add("Text", DTable, "Имя");

            comboBox1.DataSource = DTable;
            comboBox1.ValueMember = "КодСотрудника";
            comboBox1.DisplayMember = "Фамилия";
        }

        private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
        {
            string str = comboBox1.SelectedValue.ToString();
            textBox1.Text = str; // Ok!
            int number = Convert.ToInt32(str); // Error!
        }

}