round、floor、ceil、trunc的对比

结论先行：round为四舍五入，floor为最近的较小整数，ceil为最近较大整数，trunk为小数为正时为最近较小整数，为负时为最近较大整数。

示例如下：

#include <stdio.h>      #include <math.h>       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;}

输出：

value   round   floor   ceil    trunc-----   -----   -----   ----    -----2.3     2.0     2.0     3.0     2.03.8     4.0     3.0     4.0     3.05.5     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