#include <iostream>
#include <fstream>
#include <stdlib.h>
#include <string.h>
#include <math.h> 
#define MIN_DEFAULT -100
#define MAX_DEFAULT 100
#define ACCURACY_DEFAULT 0.1
#define ITERATION_MAX 100

using namespace std;
double equ(double x,double a, double b, double c){
  return a*x*x+b*x+c;
}

int output_ans(double ans,double a, double b, double c,int itt){
  cout << "answer: x="<<ans<<" y="<<equ(ans,a,b,c)<<" (after "<<itt<<" iterations)"<<endl;
  return 0;
}
//quadratic equation 1
int main(int argc, char *argv[] ){
  double a,b,c;
  double min,max,acc;
  double x_min,x_max,y_min,y_max;
  double x_mean,y_mean;
  double ans;
  int itt, itt_max;
  if(argc<4){
    cerr<< "quadra_1 a b c min max step"<< endl;
    return 1;
      }
  else{
    a=atof(argv[1]);
    b=atof(argv[2]);
    c=atof(argv[3]);
  }
  if(argc<6){
    min=MIN_DEFAULT;
    max=MAX_DEFAULT;
  }
  else{
    min=atof(argv[4]);
    max=atof(argv[5]);
  }
  if(argc<7){
    acc=ACCURACY_DEFAULT;
  }  
  else{
    acc=atof(argv[6]);
  }
  itt_max=ITERATION_MAX;

  // output the parameters
  cerr << "quadra_2 for solving quadratic equation by bisection method"<<endl;
  cerr <<"equation: "<<a<<"*x^2 + "<< b << "*x + " << c << " = 0"<<endl;
  cerr <<"ans search range: "<<min<<" : "<< max  <<endl;
  cerr << "accuracy= " << acc << ", iteration maximum="<<itt_max<<endl<<endl;

  //initialization
  x_min=min;
  x_max=max;
  y_min=equ(x_min,a,b,c);
  y_max=equ(x_max,a,b,c);
  itt=0;

  if(fabs(y_min)<acc){ //fabs for absolute value
    ans=x_min; 
    output_ans(ans,a,b,c,itt);
    return 0;
  }
  if(fabs(y_max)<acc){
    ans=x_max;
    output_ans(ans,a,b,c,itt);
    return 0;
  } 

  if(y_min*y_max>0){
    cerr <<"Signs of y(x_min) and y(x_max) are same."<<endl;
    cerr <<"Bisection method cannot be started."<<endl;
    return 1;
  }

  x_mean=(x_min+x_max)/2.;
  y_mean=equ(x_mean,a,b,c);
  
  //answer search
  while(fabs(y_mean)>acc&&itt<itt_max){
    if(y_min*y_mean<0){
      x_max=x_mean;
    }
    else{
      x_min=x_mean;
    }
    y_max=equ(x_max,a,b,c);
    y_min=equ(x_min,a,b,c);
    x_mean=(x_min+x_max)/2.;
    y_mean=equ(x_mean,a,b,c);
    itt++;
  }
  ans=x_mean;
  output_ans(ans,a,b,c,itt);

  return 0;
}