#include<stdio.h>
#include<math.h>
/*int main()
{
    int a = -10,b = 10;
    flf = 2*a*a*a-4*a*a+3*a-6;
    frg = 2*b*b*b-4*b*b+3*a-6;
    mid = (a+b)/2;
    fmid = 2*mid*mid*mid-4*mid*mid+3*mid-6;
    if(flf*frg >= 0)
        printf("原方程在区间上无根或不止一根\n");
    else
    {
        while(flf*mid < 0)
        {
            
        }
    }
}*/
int main()
{
    float a = -10,b = 10,mid,fmid,flf,frg;
    float _x=20;
    int icount = 0;
    do
    {
        flf = 2*a*a*a-4*a*a+3*a-6;
        frg = 2*b*b*b-4*b*b+3*a-6;
        //if(flf*frg >= 0)
        //{
        //printf("原方程在区间上无根或不止一根\n");
        //break;
        //}
        mid = (a+b)/2;
        fmid = 2*mid*mid*mid-4*mid*mid+3*mid-6;
        if((flf*fmid) < 0)
        {
            b = mid;
        }
         if((fmid*frg)<0)
        {
            a = mid;
        }
         //if(fabs(fmid)< 1e-6)
            // break;
        _x= b-a;
        //printf("%f\n",_x);
        icount++;
        
    }while(_x > 1e-2);
        printf("The root is %f\n",(a+b)/2);
        printf("%d\n",icount);
}
//想用二分法求方程2x^3 - 4x^2 + 3x - 6 = 0 在[-10，10]上的根，达不到目的（改小1e-2也没用），跪求高手指点

本人觉得是精度问题，flf*frg<0这个条件无法判断两者是否异号，望大神指导

谢谢版主了，一个用宏，一个用函数，函数指针有必要吗。难道double就把精度问题解决了？soga分数补上，谢啦！