Try like this.
if this is your exact need, then this will help you.
SqlDataAdapter da = new SqlDataAdapter(myCommand);
da.Fill(dt);
if (dt.Rows.Count == 1)
{
DataRow row = dt.Rows[0];
for (int i = 0; i < 20; i++)
{
string value = row[i] + "";
(Page.FindControl("TextBox" + i) as TextBox).Text = value; ;
}
}