Метод половинного деления

#include <iostream>
#include <cmath>
using namespace std;
 
float f(float x)
{
  return x / x * x * x * x - 2;
}
 
float n(float x1, float x2)
{
  float x = (x2 + x1) / 2;
  while (abs(f(x)) > 0.001)
  {
    if (f(x) > 0)
      x2 = x;
    else 
      x1 = x;
    x = (x2 + x1) / 2;
  }
  return x;
}
 
int main()
{
  cout << n(0, 100) << endl;
}

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
 
double polynom_fn(vector<double> &koeff, double x)
{
double ret_val=koeff[0];
int rate=koeff.size();
for(int i=1; i<rate; ++i)
{
ret_val+=pow(x, i)*koeff[i];
}
return ret_val;
}
 
double bin_div_sol(double (*fun)(vector<double> &, double), vector<double> &koeff, double x1, double x2, double eps=1.e-4 )
{
double  x=(x1+x2)/2, y1=(*fun)(koeff, x1), y2=(*fun)(koeff, x2), y=(*fun)(koeff, x), y_prev=y;
if(abs(y1)<eps) return x;
do{
    if((y>0 && y1>0) || (y<0 && y1<0))
    { 
        x1=x;
             y1=(*fun)(koeff, x1);
    }else
    {
        x2=x;
            y2=(*fun)(koeff, x2);
    }
 
        x=(x1+x2)/2; 
            y_prev=y;
                y=(*fun)(koeff, x);
 
    }while( abs(y_prev-y) > eps );
 
return x;
}
 
int main(int argc, char* argv[])
{
 
//vector<double> koeff;
//int deg
//cout<<"input the polynomial degree";
//cin>>deg;
//deg++;
//floar k;
//for(int i=0; i<deg; ++i)
//{
//cout<<"Type the koef No "<<i<<' ';
//cin>>k;
//koeff.push_back(k);
//}
//отладочный массив
int sk=3;   double k[]={-10., 2., 1.}; 
vector<double> koeff(k, k+sk);
double x1, x2;
cout<<"enter the working interval limits\n"<<endl;
cout<<"x1= ";
cin>>x1;//0
cout<<"x2= ";
cin>>x2;//10
if(x1>x2)swap(x1,x2);
if(polynom_fn(koeff, x1)*polynom_fn(koeff, x2)<0)//значения функции в разных концах интервала должны
//отличаться по знаку
{
double solution =  bin_div_sol( polynom_fn, koeff, x1,x2 );
cout.precision(5);
cout<<"solution is x= "<<solution<<endl;//2,3166
}
else
{
cout<<"no solution found";
}
cout<<endl;
system("pause");
return 0;
}

//somwere upon a story:
double epsil;
cout<<"ep?  ";
cin>>epsil;
//--------------something else-----------
bin_div_sol( polynom_fn, koeff, x1,x2, epsil );