//****************************************************************
//
//    Program to illustrate functions.  Calculates square root.
//       L.Aamodt  2/03/16
//
//****************************************************************

#include <iostream>

using namespace std;

//    Prototypes of functions
double our_sqrt(double x);
double our_abs(double value);

int main()
{
    double number;

    do
    {
    cout << "Enter a value: ";
    cin >> number;
    if (number > 0)
        cout << "square root = " << our_sqrt(number) << "\n\n";
    else if (number < 0)
        cout << "can't handle a negative #\n";
    }
    while (number != 0);

    cout << "done\n";
    return 0;
}

//  ****  Square root function ****
double our_sqrt(double x)
{
    double guess=2.0, epsilon=.00001;

    while (our_abs((guess*guess/x)-1) > epsilon)
        guess = guess + (1-guess*guess/x)/2;

    return(guess);
}

//  **** Absolute function ****
double our_abs(double value)
{
    if (value < 0)
        value = -value;
    return(value);
}