对浮点数进行四舍五入
>>> $price = 100.8875;
=> 100.8875
>>> round($price, 2) // 保留两位小数
=> 100.89
>>> round($price, 0)
=> 101.0
>>> $price = 100.1815;
=> 100.1815
>>> round($price, 2) // 保留两位小数
=> 100.18
>>> round($price, 0)
=> 100.0
>>> round(1.1) // 简写
=> 1.0
向上取整
>>> ceil(1.1)
=> 2.0
向下取整
>>> floor(1.1)
=> 1.0