binary search algorithm pattern

$time\ O(logn)$

#include<iostream>
using namespace std;

int main()
{
    double n;
    cin>>n;
    double l=-10000.0,r=10000.0;
    while(abs(l-r)>1e-9)
    {
        double mid=(l+r)/2;
        if(mid*mid*mid-n>=1e-9) r=mid;
        else l=mid;
    }
    printf("%.6f",l);
    return 0;
}