static void Main(string[] args)
{
DaThuc A = new DaThuc();
A.Nhap();
A.xuat();
DaThuc B = new DaThuc();
B.Nhap();
B.xuat();
DaThuc C = new DaThuc();
C = A + B;
Console.WriteLine("Tong da thuc la:{0}", C);
C = A - B;
Console.WriteLine("Hieu da thuc la:{0}", C);
Console.ReadLine();
}
