Math.Round：四舍六入五取整

Math.Ceiling：向上取整，只要有小数都加1

Math.Floor：向下取整，总是舍去小数

aa = Convert.ToInt32(Math.Ceiling(a/ c) );
bb = Convert.ToInt32(Math.Ceiling(b/ c) );
int z = (int)Math.Ceiling((double) a/ c);