P1024 [NOIP2001 提高组] 一元三次方程求解

WA求助

#include<bits/stdc++.h>
using namespace std;
#define eps 1e-4
double a,b,c,d;
double f(double x)
{
	return a*x*x*x+b*x*x+c*x+d;
}
int main()
{
	cin>>a>>b>>c>>d;
	for(register int i=-100;i<=100;i++)
	{
		double l=i;
		double r=i+1;
		if(fabs(f(l))<eps) printf("%.2f ",l);
		else if(fabs(f(r))<eps) continue;
		else if(f(l)*f(r)<0)
		{
			while(r-l>eps)
			{
				int mid=(l+r)>>1;
				if(f(mid)==0) r=mid;
				else l=mid;
			}
			printf("%.2f ",l);
		}
	}
    return 0;
}