C-例8-6 二分法求方程的根

f(x)=pow(x,3)-5*pow(x,2)+16*x-80=0的根

#include<stdio.h>
#include<math.h>
#define F(x) ((x-5.0)*x+16.0)*x-80.0
float root(float x1,float x2);
int main()
{
	float x1,x2,final,f1,f2;
	do
	{
		scanf("%f%f",&x1,&x2);
		f1=F(x1);
		f2=F(x2);
	}while(f1*f2>0);
	final=root(x1,x2);
	printf("%.2f",final);
}
float root(float x1,float x2)
{
	float mid;
	mid=(x1+x2)/2.0;
	if(F(mid)==0.0)
		return mid;
	while(fabs(F(mid))>=0.0001)
	{
		mid=(x1+x2)/2.0;
		if(F(mid)>0)
			x2=mid;
		else 
			x1=mid;
	}
	return mid;
}