// Bisection Version 2
#include <iostream>
#include <cmath>
using namespace std;

double f( double x )
{
    return( x * x - 2.0 );
}

int main()
{
// User input ******************************
    double x1 = 1.0;
    double x2 = 3.0;
    const double TOLERANCE = 1.0e-9;
    const int MAX_ITERS = 150;
// *****************************************
    
    double fx1 = f(x1), fx2 = f(x2), xp, xn, m, fm, error;
    int count = 0;
    cout.precision( 8 );
    
    if ( fx1 * fx2 < 0.0 ) {        
        ( fx1 > 0 ) ? ( xp = x1, xn = x2 ) : ( xp = x2, xn = x1 );
        do {
            m = ( xn + xp ) / 2.0;
            if ( ++count > MAX_ITERS ) {
                cout << "STOP: Maximum numbers of iterations exceeded.\n"
                     << "Desired accuracy was probably not achieved.\n";
                     break;
            }
            if ( ( fm = f(m) ) == 0.0 ) {
                cout << "Congratulations! You have found the exact solution.\n";
                xn = m, xp = m;
                break;
            }
            ( fm > 0.0 ) ? xp = m : xn = m;
            error = abs( xp - xn );
        } while ( error > TOLERANCE );
        cout << "Your solution is: x = " << ( xn + xp ) / 2.0;
    }
    else
        cout << "STOP: Signs of f are not different at startup.\n"
             << "Check your interval.\n";
    
    cout << "\n\n"; system( "PAUSE" );
    return( 0 );
}