c语言编程练习题：7-29 二分法求多项式单根

#include <stdio.h>

double fv(double a3,double a2,double a1,double a0,double x){

   double value = a3*x*x*x + a2*x*x + a1*x + a0;

   return value;

}

double solve_equation(double a3,double a2,double a1,double a0,double a,double b){

       double mid;

       double fa,fb,fm;

       fa = fv(a3,a2,a1,a0,a);

       fb = fv(a3,a2,a1,a0,b);

       if (fa==0){return a;}

       if (fb==0){return b;}

       while (fa*fb<0){

           fa = fv(a3,a2,a1,a0,a);

           fb = fv(a3,a2,a1,a0,b);

           mid = (a+b)/2;

           fm = fv(a3,a2,a1,a0,mid);

           //printf("%lf %lf %lf %lf %lf\n",a,b,fa,fb,fm);

           if (fm<=0.0001 && fm>=-0.0001){return mid;}

           else{

               if (fm*fb<0){a=mid;}

               if (fm*fa<0){b=mid;}

           }

       }

   while (fa*fb>0){return 9999999;}

}

int main(){

   double a3,a2,a1,a0,a,b;

   if (scanf("%lf %lf %lf %lf %lf %lf",&a3,&a2,&a1,&a0,&a,&b)!=0){

       //printf("%lf %lf %lf %lf %lf %lf\n",a3,a2,a1,a0,a,b);

       double r;

       r = solve_equation(a3,a2,a1,a0,a,b);

       printf("%.2lf",r);

   }else{

       printf("something wrong");

   }

   return 0;

}