小数有效位

//保留两位小数，四舍五入
CGFloat rounded_up = round(0.355 * 100) / 100;
NSLog(@"%.2lf",rounded_up);

//保留两位小数，直接进1(天花板函数)
CGFloat rounded_up1 = ceilf(0.355 * 100) / 100;
NSLog(@"%.2lf",rounded_up1);

//保留两位小数，舍弃后面所有位数。(地板函数)
CGFloat rounded_up2 = floor(0.355 * 100) / 100;
NSLog(@"%.2lf",rounded_up2);