static void Main(string[] args)
{
Suma s1 = new Suma();
Resta r1 = new Resta();
Producto p1 = new Producto();
s1.Nro1 = 15;
s1.Nro2 = 10;
s1.operar();
s1.imprimir();
r1.Nro1 = 10;
r1.Nro2 = 16;
r1.operar();
r1.imprimir();
p1.Nro1 = -10;
p1.Nro2 = 11;
p1.operar();
p1.imprimir();
Console.ReadKey();
}