我用的是Dev-c++，编写程序如下：
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double f(double x)
{
    double y;
    y=x*x*x*x+4*x*x*x-3*x*x+5*x+6;
    return(y);
    }
double point(double x1, double x2)
{
    double x;
    double y1;
    double y2;
    y1=f(x1);
    y2=f(x2);
    x=(x1*y2-x2*y1)/(y2-y1);
    return(x);
    }
double root(double x1, double x2)
{
       double x;
       double y;
       double y1;
       y1=f(x1);
       do
       {
                          x=point(x1, x2);
                          y=f(x);
                          if(y*y1>0)
                          {
                                    x1=x;
                                    y1=y;
                                    }
                          else
                          x2=x;
                             }
                             while(fabs(y)>=1e-9);
                             return(x);
       }
int main(int argc, char *argv[])
{
  double x1;
  double x2;
  double r;
  double y1;
  double y2;
  do
  {
         printf("请输入两个数：\n");
         scanf("%lf%lf", &x1, &x2);
         y1=f(x1);
         y2=f(x2);
         }while((y1*y2)>=0);
  r=root(x1, x2);
  printf("该方程的根为: r=%lf\n");
  system("PAUSE");   
  return 0;
}
输入10 和-2，运行结果不正确，为：该方程的根为：r=-44686712925511037000000000000000000000000000000000000000000000000

请各位大侠帮忙分析一下我哪里出错了，不胜感激！！！

printf("该方程的根为: r=%lf\n", r);

多谢楼上的兄弟。