# include <cstdlib>
# include <iostream>
# include <cmath>

using namespace std;

int main ( )
//
//  SQROOT_CHECK estimates a square root, and checks that the number
//  of steps is not too large.
//
//  We need to include <cmath> because we are using the fabs() function.
//
//  The error tolerance is too small for floating point arithmetic
//  when the input value is 700, for instance.
//
{
  float error, h, w, x;
  int step;

  cout << "Input the number whose square root is desired: ";
  cin >> x;
//
//  Initialization.
//
  h = x;
  w = x / h;
  error = x - h * h;
  step = 0;
//
//  Loop.
//
  while ( 0.000001 < fabs ( error ) )
  {
//
//  Increase the loop counter.
//
    step = step + 1;

    if ( 100 < step )
    {
      cerr << "\n";
      cerr << "Failure!\n";
      cerr << "  Too many steps!\n";
      cerr << "  Square root estimate is " << h << "\n";
      cerr << "  Error is " << error << "\n";
      exit ( 1 );
    }
    h = ( h + w ) / 2.0;
    w = x / h;
    error = x - h * h;
  }
//
//  We exited the loop, because our estimate beat the error estimate.
//
  cout << "\n";
  cout << "Success!\n";
  cout << "  Square root estimate is " << h << "\n";
  cerr << "  Error is " << error << "\n";

  return 0;
}