C++学习之floor函数,ceil函数和round函数

做题时经常需要截断小数点，向上取整或者向下取整，以前使用printf（"%.2f",n）;进行截断操作，但如果数据不需要输出，这种做法就行不通了，此时可以使用floor函数向下取整或者ceil函数向上取整。

头文件：#include<cmath>

一.floor() 函数（向下取整）

1、函数原型：

double floor ( double x );
float floor ( float x );
long double floor ( long double x );

2、功能：返回一个小于传入参数的最大整数

3、参数：x为将来被处理的数

4、返回值：返回不大于x的最大整数

5、注在C语言中只有double一个原型

6、示例程序

#include <cstdio>
#include <cmath> 
int main ()
{
	printf ("floor of 2.3 is %.1lf/n", floor (2.3) );
	printf ("floor of 2.6 is %.1lf/n", floor (2.6) );
	printf ("floor of -2.3 is %.1lf/n", floor (-2.3) );
	printf ("floor of -2.6 is %.1lf/n", floor (-2.6) );
	return 0;
}

输出:

floor of 2.3 is 2.0
floor of 2.6 is 2.0
floor of -2.3 is -3.0
floor of -2.6 is -3.0

二.ceil()函数(向上取整)

1、函数原型:

double ceil ( double x );
float ceil ( float x );
long double ceil ( long double x );

2、功能：返回一个大于传入参数的最小整数

3、参数：x为将来被处理的数

4、返回值：返回不小于x的最小整数

5、注在C语言中只有double一个原型

6、示例程序

#include <cstdio>
#include <cmath> 
int main ()
{
	printf ("ceil of 2.3 is %.1lf/n", ceil (2.3) );
	printf ("ceil of 2.6 is %.1lf/n", ceil (2.6) );
	printf ("ceil of -2.3 is %.1lf/n", ceil (-2.3) );
	printf ("ceil of -2.6 is %.1lf/n", ceil (-2.6) );
	return 0;
}

输出:

ceil of 2.3 is 3.0
ceil of 2.6 is 3.0
ceil of -2.3 is -2.0
ceil of -2.6 is -2.0

三.round()函数（四舍五入）

C++中没有round函数，需要自己建立（或者直接用floor函数和ceil函数模拟）。

示例程序：

#include <cstdio>
#include <cmath>
 double round(double r){
    return (r > 0.0) ? floor(r + 0.5) : ceil(r - 0.5);
}
int main ()
{
    printf ("round of 2.3 is %.1lf/n", round (2.3) );
    printf ("round of 2.6 is %.1lf/n", round (2.6) );
    printf ("round of -2.3 is %.1lf/n", round (-2.3) );
    printf ("round of -2.6 is %.1lf/n", round (-2.6) );
    return 0;
}

示例程序输出:

round of 2.3 is 2.0
round of 2.6 is 3.0
round of -2.3 is -2.0
round of -2.6 is -3.0

来源：CSDN

作者：小·幸·运

链接：https://blog.csdn.net/vir_lee/article/details/80573096

标签

取整函数

floor

ceil