50分萌新求助，求大神指点

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <map>
#define nmax 100100
#define LL unsigned long long 
using namespace std;
double a,b,c,d,mid;
double f(int x){
    return a*x*x*x+b*x*x+c*x+d;
}
void erfen(double l,double r){
    while(abs(r-l)>0.001){
        mid=(l+r)/2;
        if(f(mid)*f(r)<=0){
            l=mid;
        }
        else{
            r=mid;
        }
    }
    printf("%.2lf ",l);
    return ;
}
int main(){
    cin>>a>>b>>c>>d;
    for(int i=-100;i<100;i++){
        if(f(i)==0){
            float mmqm;
            mmqm=(float)i;
            printf("%.2f ",mmqm);
            break;
        }
        if(f(i)*f(i+1)<=0){
            erfen(i,i+1);
            i++;
        }    
    }
    return 0;
}