向上取整ceil()

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

向上取整,返回大于等于x的值.

示例:

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#include <stdio.h>      /* printf */
#include <math.h>       /* 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;
}

向下取整floor

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

向下取整,返回小于等于x的值

示例:

#include <stdio.h>      /* printf */
#include <math.h>       /* 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;
}

绝对值abs,labs,llabs,fabs

abs

      int abs (          int n);
 long int abs (     long int n);
long long int abs (long long int n);

返回n的绝对值

示例:

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#include <stdio.h>      /* printf */
#include <stdlib.h>     /* abs */

int main ()
{
  int n,m;
  n=abs(23);
  m=abs(-11);
  printf ("n=%d\n",n);
  printf ("m=%d\n",m);
  return 0;
}

labs

long int labs (long int n);

示例:

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#include <stdio.h>      /* printf */
#include <stdlib.h>     /* labs */

int main ()
{
  long int n,m;
  n=labs(65537L);
  m=labs(-100000L);
  printf ("n=%ld\n",n);
  printf ("m=%ld\n",m);
  return 0;
}

llabs

long long int llabs (long long int n);

示例:

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#include <stdio.h>      /* printf */
#include <stdlib.h>     /* llabs */

int main ()
{
  long long int n,m;
  n=llabs(31558149LL);
  m=llabs(-100000000LL);
  printf ("n=%lld\n",n);
  printf ("m=%lld\n",m);
  return 0;
}

fabs

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

示例:

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#include <stdio.h>      /* printf */
#include <math.h>       /* fabs */

int main ()
{
  printf ("The absolute value of 3.1416 is %f\n", fabs (3.1416) );
  printf ("The absolute value of -10.6 is %f\n", fabs (-10.6) );
  return 0;
}

sqrt

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

计算平方根 返回x的平方根。

示例:

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

int main ()
{
  double param, result;
  param = 1024.0;
  result = sqrt (param);
  printf ("sqrt(%f) = %f\n", param, result );
  return 0;
}