数学运算中的四舍五入

分函数
#include<math.h>
double mathround(double num,int n)
{
     long d;
     if(n<0){
         return num;
     }
     if(num>=0.0)
     {
          d=(num*pow(10,n))+0.5;
     }
     else
     {
          d=(num*pow(10,n))-0.5;
     }
     return d/pow(10,n);
}
主函数
#include"util_math.h"

int main(int argc,char *argv[])
{
 double num=-12345.6789,num1;
 int m=2;
 printf("the former num is %lf\n",num);
 num1=mathround(num,m);
 printf("the mathround num is %lf\n",num1);
 exit(0);
}