static void Main(string[] args)
{
SOTHUC t1 = new SOTHUC(1, 2);
t1.hien();
SOTHUC t2 = new SOTHUC(3, 4);
t2.hien();
Console.WriteLine("tong 2 so thuc");
SOTHUC t3 = t1 + t2;
t3.hien();
Console.WriteLine("hieu 2 so thuc");
SOTHUC t4 = t1 - t2;
t4.hien();
Console.ReadKey();
}