Comparison of several number rounding methods

Source code:

/* floor example */
#include <stdio.h>      /* printf */
#include <math.h>       /* floor */

#define ROUND(x) ((x < 0) ? (x - 0.5f) : (x + 0.5f))

int main ()
{
  
  printf ("---------------------------\n");
  printf ( "floor of 2.3 is %d\n", (int) (2.3) );
  printf ( "floor of 3.8 is %d\n", (int) (3.8) );
  printf ( "floor of -2.3 is %d\n", (int) (-2.3) );
  printf ( "floor of -3.8 is %d\n", (int) (-3.8) );
  
  printf ("---------------------------\n");
  printf ( "floor of 2.3 is %d\n", (int)floor (2.3) );
  printf ( "floor of 3.8 is %d\n", (int)floor (3.8) );
  printf ( "floor of -2.3 is %d\n", (int)floor (-2.3) );
  printf ( "floor of -3.8 is %d\n", (int)floor (-3.8) );
  
  printf ("---------------------------\n");
  printf ( "floor of 2.3 is %d\n", (int)ceil (2.3) );
  printf ( "floor of 3.8 is %d\n", (int)ceil (3.8) );
  printf ( "floor of -2.3 is %d\n", (int)ceil (-2.3) );
  printf ( "floor of -3.8 is %d\n", (int)ceil (-3.8) );
  
  printf ("---------------------------\n");
  printf ( "floor of 2.3 is %d\n", (int)ROUND (2.3) );
  printf ( "floor of 3.8 is %d\n", (int)ROUND (3.8) );
  printf ( "floor of -2.3 is %d\n", (int)ROUND (-2.3) );
  printf ( "floor of -3.8 is %d\n", (int)ROUND (-3.8) );
  
  return 0;
}

Result:

Conclusion:

1. (int) just truncate the integer part of a float number;

2. floor and ceil rounds number downward and upward respectively.

3. By adding a 0.5 use (int) to truncate, we can get the closest integer to the original number.