大家看下这个题目

/*

 * File Name: Easy.cpp

 * Date: 2010/12/21

 * Auto: ZhouFeng

 */

#include <iostream>
#include <iomanip>

using std::cout;
using std::endl;
using std::cin;
using std::setiosflags;
using std::ios;
   
const double END_RECURSION = 0.00001;                // 循环结束条件
   
double CountX( double, double, double);           
double FloatAbs( double);                            // 计算double类型绝对值

int main()
{
    while( true)
    {
        cout << "Please enter the value of A:\n";
        double A;
        cin >> A;
        double result = CountX( 1, 2, A);
      
        cout << setiosflags( ios::fixed) << std::setprecision(3) << result << endl;
    }
   
    return 0;
}

double CountX( double preX, double lstX, double a)
{
    while( true)
    {
        lstX =  ( preX + a / preX) / 2;
        if ( FloatAbs( preX - lstX) > END_RECURSION)
        {
            preX = lstX;
            lstX = ( preX + a / preX) / 2;
        }
        else
        {
            break;   
        }
    }
   
    return preX;
}

double FloatAbs( double num)
{
    double res = num;
   
    if( num < 0)
    {
        res = -1 * res;
    }
   
    return res;
}