int[] a = new int[10]; int i;
        private void Form1_Load(object sender, EventArgs e)
        {
            label1.Text = "逆反前的数字顺序是：\n";
            for (i = 0; i < a.Length; i++)
            {
                a[i] = i;
                label1.Text = label1.Text+a[i].ToString() + ",";
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            label2.Text = "逆反后的顺序是：\n";
            for (i = a.Length - 1; i <=0;i-- )
            {
                label2.Text = label2.Text + Convert.ToString(a[i]) + ",";
            }
        }

for (i = a.Length - 1; i <=0;i-- )
是 i >= 0 吧

谢谢啊。前辈。