private void cmbFloorNo_SelectedIndexChanged(object sender, EventArgs e)
{
//Create a database object to get the list of departments
LibraryDB dbInfo = new LibraryDB();
List <String> shelfList = new List <String>();
shelfList = dbInfo.getShelfNums(Int32.Parse(cmbFloorNo.Text));
cmbShelfNo.DataSource = shelfList;
}