学步园

    //源自于一个大神级回复 
//连接：http://topic.csdn.net/u/20120111/16/68047c3d-e8dd-479b-b17d-9858302e4a0f.html?r=77297489

      public static double foo(double d, int n)
        {
            if (d == 0.0) return 0;
            if (d > 1 || d < -1)
                n = n - (int)Math.Log10(Math.Abs(d)) - 1;
            else
                n = n + (int)Math.Log10(1.0 / Math.Abs(d));
            if (n < 0)
            {
                d = (int)(d / Math.Pow(10, 0 - n)) * Math.Pow(10, 0 - n);
                n = 0;
            }
            return Math.Round(d, n);
        }