binding combo box text to text box

Hi,mani
  You write your code at combobox selectedindexchanged event

as follows

first adapt.fill (dst,"stud")

if(dss.Tables["stud"].Rows.Count>0)
 { textBox1.Text=dss.Tables["stud"].Rows[0]["studno"].ToString(); }

or

  use below site for reference

http://msdn.microsoft.com/en-us/library/system.windows.forms.combobox.selectedindexchanged.aspx[^]

Hope you help