1、round()遵循四舍五入把原值转化为指定小数位数。如:round(1.45,0) = 1;round(1.55,0)=22、floor()向下舍入为指定小数位数.如:floor(1.45,0)= 1;floor(1.55,0) = 13、ceiling()向上舍入为指定小数位数.如:ceiling(1.45,0) = 2;ceiling(1.55,0)=2