private void button1_Click(object sender, EventArgs e)
        {
            int n1 = int.Parse(textBox1.Text);
            int n2 = int.Parse(textBox2.Text);

            Dollar dollar1 = new Dollar(n1);
            Dollar dollar2 = new Dollar(n2);
            Dollar total = new Dollar(0);
            total = dollar1 + dollar2;

            string msg = dollar1.ToString() + "+" + dollar2.ToString();
            msg += "=" + total.ToString();
            MessageBox.Show(msg,"計算");
        }
        private void button1_Click(object sender, EventArgs e)
        {
            int n1 = int.Parse(textBox1.Text);
            int n2 = int.Parse(textBox2.Text);

            Dollar dollar1 = new Dollar(n1);
            Dollar dollar2 = new Dollar(n2);
            Dollar total   = new Dollar(0);

            total = dollar1 + dollar2;

            string msg = dollar1.ToString() + "+" + dollar2.ToString();

            msg += "=" + total.ToString();
            MessageBox.Show(msg, "計算");
        }