#include <library.h>

const bool debug = true;

double find_sqrt(const double k,
                 const double min_pos,
                 const double max_pos)
{ if (debug)
    cout << setprecision(20) << min_pos << "  " << max_pos << "\n";
  const double error = max_pos - min_pos;
  const double guess = (min_pos + max_pos) / 2;
  if (debug)
    cout << "err=" << error << ", err/guess=" << error/guess << "\n";
  if (error/guess < 1.0e-14)
    return guess;
  if (debug)
    cout << "g=" << guess << " " << guess*guess << "\n\n";
  if (guess*guess == k)
    return guess;
  if (guess*guess > k)
    return find_sqrt(k, min_pos, guess);
  else
    return find_sqrt(k, guess, max_pos);
}


void main()
{ while (true)

  { cout << "search for: ";
    const double w = read_double();

    const double p = find_sqrt(w, 0, w + 1);

    cout << "the square root of " << w << " is " << p << "\n"; } }