C#

private void comboBox1_TextChanged(object sender, EventArgs e)
        {
            int j = 0;
            string str,strTemp,str1;
            str = comboBox1.Text; 
            comboBox1.Items.Clear();            
            for (int i = 0; i < List.Count; i++)
            {
                j++;
                string value = List[i] as string;              
                str1 = value.ToUpper();
                strTemp = str.ToUpper();
                if (str1.IndexOf(strTemp) != -1)
                {
                    j++;
                    comboBox1.Items.Add(value);
                }
            }
            
            int k = str.Length;    
            comboBox1.Select(k, k++);            
            comboBox1.DroppedDown = true;
           
        }

con = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=practicedatabase.accdb");
                con.Open();
                string qry = "Select * from cat_table";
                dadapter = new OleDbDataAdapter(qry, con);
                dset = new DataSet();
                DataTable dt = new DataTable("cat_table");
                dadapter.Fill(dt);
                this.comboBox1.DataSource = dt;
                this.comboBox1.DisplayMember = dt.Columns[1].ColumnName;