好吧，既然这么多人都不理解的话，那本人就勉强发一篇关于此题的题解吧

#include<bits/stdc++.h>
using namespace std;
double a,b,c,d,s;
double fc(double x){
	return a*x*x*x+b*x*x+c*x+d;
}
int main(){
	double l,r,m,x1,x2;
	scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
	for(int i = -100;i<100;i++){
		l = i; 
		r = i+1;
		x1 = fc(l); 
		x2 = fc(r);
		if(!x1){
			printf("%.2lf ",l); 
			s++;
		}
		if(x1*x2<0){
			while(r-l>=0.001){
				m = (l+r)/2;
				if(fc(m)*fc(r)<=0)l = m; 
				else r = m;
			}
			printf("%.2lf ",r);
			s++;
		}
		if(s == 3)break;
	}
	return 0;
}