一元三次方程

#include <bits/stdc++.h>

using namespace std;
double a,b,c,d;
double fun(double x)
{
    return a*x*x*x+b*x*x+c*x+d;
}
int main()
{
    double x1,x2,xx;
    int i;
   cin>>a>>b>>c>>d;
    for(i=-100;i<=100;i++){
        x1=i,x2=i+1;
        if(fun(x1)==0){
            printf("%.2f ",x1);
        }
        else if(fun(x1)*fun(x2)<0){
            while(x2-x1>=0.001){
                xx=(x1+x2)/2;
                if((fun(x1)*fun(xx))<=0) x2=xx;
                else x1=xx;
            }
            printf("%.2f ",x1);
        }
    }
    return 0;
}