public string Mostrar()
        {
            //if (EstaVacia())
            //{
            //    return "Pila Vacia...";
            //}
            string salida =this.top==this.max?"\tMAX=T\n":"\tMAX\n";
            int maxCaracteres = MaxLength();
            for (int i = this.max-1; i >= 0; i--)
            {
                salida += i + " | ";//colocando indice del renglon
                int avance=i<this.top?this.arreglo[i].ToString().Length:0;

                for (int j = avance; j < maxCaracteres; j++)
                    salida += " ";
                //esto vvv
                if (i<this.top)
                    salida += this.arreglo[i] + " |"; //inserta valor

                else
                    salida += " | ";
                //es lo mismo que esto vvv
                //salida+=i<this.top?this.arreglo[i]+" | ": salida+=" | ";

                if (i == this.top)
                    salida += " T\n";//colocando Top
                else
                    salida += "\n";

            }
            return salida;
        }
        private int MaxLength()
        {
            int maxCaracteres = int.MinValue;
            for (int j = 0; j < this.top; j++)
                if (maxCaracteres < this.arreglo[j].ToString().Length)
                    maxCaracteres = this.arreglo[j].ToString().Length;

            return maxCaracteres;
        }