Console.Write(f <= 0.0f ? ".:-=+*#%@"[(int)(f* -8.0f)] : ' ');

初学者，麻烦大神看看下面这段c#程序啥意思啊

float y, x, z, f;
            for (y =1.5f; y > -1.5f; y -= 0.1f)
            {
                for (x = -1.5f; x < 1.5f;x += 0.05f)
                {
                    z = x * x + y * y - 1;//不懂
                    f = z * z * z - x * x * y * y * y;//不懂
                    Console.Write(f <= 0.0f ? ".:-=+*#%@"[(int)(f* -8.0f)] : ' ');//不懂
                }
                Console.WriteLine();
            }
        }
    }
}