用C#的WindForm窗体编写程序:矩形输入宽和高，输出面积

private int f(int i) { if (i == 1) { return 1; } else { return f(i - 1) + g(i); } } private int g(int i) { if (i == 1) { return 1; } else { return g(i - 1) * i; } } private void button1_Click(object sender, EventArgs e) { int n = Convert.ToInt32(textBox1.Text); textBox2.Text = f(n).ToString(); }