public void play(bool m)
        {
            string str = "";//定义一个变量str用来获取照片的名字;
            if(m )
            {
                a++;
                int n = 0;//n表示实际照片的个数;
                if (a < 0)
                {
                    n = Math.Abs(a) % 9;                }
                else
                {
                    n = a %9;
                }
                str = "Images/" + n + ".jpg";
            }
             else
            {
                a--;
                int n = 0;
                if (a < 0)
                {
                    n = Math.Abs(a + 9) % 9;
                }
                else
                {
                    n = a % 9;
                }
                str = "Images/" + n + ".jpg";
            }
这个代码看不懂什么意思 谁能帮我一句句的解释一下 谢谢啦