c++四舍五入函数，向上取整，向下取整函数

2024-07-17 03:09| 来源: 网络整理| 查看: 265

对含有小数点的数进行四舍五入是比较普遍的一种需求。在C++中也有类似的取整函数。在C++的头文件中有floor()和ceil()函数。在STL中还有round()函数。这三个函数的作用如下：

函数名称函数说明2.12.9-2.1-2.9Floor()不大于自变量的最大整数22-3-3Ceil()不小于自变量的最大整数33-2-2Round()四舍五入到最邻近的整数23-2-3

从函数说明中可以看出，（1） Floor()会取不大于自变量的最大整数，这样自变量是3.1或3.9是没有区别的，返回都是3；自变量是-2.1或-2.9也是没有区别的，返回都是-3；（2） Ceil()会取不小于自变量的最大整数，这样自变量是3.1或3.9，返回都是4；自变量是-2.1或-2.9，返回的都是-2；（3） Round()函数，才是我们需要的四舍五入的函数，因为它会返回离自变量最近的整数，这个返回的整数可能大于也可能小于原来的数，但是一定是离它最近的那个整数。

double floor (double x); float floor (float x); long double floor (long double x); double floor (T x); // additional overloads for integral types

1 2 3 4 5 6 7 8 9 10 11 12 /* floor example */ #include /* printf */ #include /* floor */ int main () { printf ( "floor of 2.3 is %.1lf\n", floor (2.3) ); printf ( "floor of 3.8 is %.1lf\n", floor (3.8) ); printf ( "floor of -2.3 is %.1lf\n", floor (-2.3) ); printf ( "floor of -3.8 is %.1lf\n", floor (-3.8) ); return 0; } Output:

floor of 2.3 is 2.0 floor of 3.8 is 3.0 floor of -2.3 is -3.0 floor of -3.8 is -4.0 double ceil (double x); float ceil (float x); long double ceil (long double x); double ceil (T x); // additional overloads for integral types 1 2 3 4 5 6 7 8 9 10 11 12 /* ceil example */ #include /* printf */ #include /* ceil */ int main () { printf ( "ceil of 2.3 is %.1f\n", ceil(2.3) ); printf ( "ceil of 3.8 is %.1f\n", ceil(3.8) ); printf ( "ceil of -2.3 is %.1f\n", ceil(-2.3) ); printf ( "ceil of -3.8 is %.1f\n", ceil(-3.8) ); return 0; } Output: ceil of 2.3 is 3.0 ceil of 3.8 is 4.0 ceil of -2.3 is -2.0 ceil of -3.8 is -3.0 double round (double x); float round (float x); long double round (long double x); double round (T x); // additional overloads for integral types /* round vs floor vs ceil vs trunc */ #include /* printf */ #include /* round, floor, ceil, trunc */ int main () { const char * format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n"; printf ("value\tround\tfloor\tceil\ttrunc\n"); printf ("-----\t-----\t-----\t----\t-----\n"); printf (format, 2.3,round( 2.3),floor( 2.3),ceil( 2.3),trunc( 2.3)); printf (format, 3.8,round( 3.8),floor( 3.8),ceil( 3.8),trunc( 3.8)); printf (format, 5.5,round( 5.5),floor( 5.5),ceil( 5.5),trunc( 5.5)); printf (format,-2.3,round(-2.3),floor(-2.3),ceil(-2.3),trunc(-2.3)); printf (format,-3.8,round(-3.8),floor(-3.8),ceil(-3.8),trunc(-3.8)); printf (format,-5.5,round(-5.5),floor(-5.5),ceil(-5.5),trunc(-5.5)); return 0; } Output: value round floor ceil trunc ----- ----- ----- ---- ----- 2.3 2.0 2.0 3.0 2.0 3.8 4.0 3.0 4.0 3.0 5.5 6.0 5.0 6.0 5.0 -2.3 -2.0 -3.0 -2.0 -2.0 -3.8 -4.0 -4.0 -3.0 -3.0 -5.5 -6.0 -6.0 -5.0 -5.0 具体可查看文献：http://www.cplusplus.com/reference/cmath/round/

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