Newton-Raphson square root implementation

sqrt.cpp

double root_NR(double n, double epsilon=.0000000001)
{
    if (n < 0) return 0.0; // throw?

    // http://mathworld.wolfram.com/SquareRootAlgorithms.html
    // Both Bhaskara-Brouncker and Newton's iteration use
    // (1 + n) / 2 instead of just guessing n/2.
    double r = 0.5 + 0.5 * n; 
    double f = r*r - n;
    while (epsilon < abs(f))
    {
        printf("%2.9f\n", r);
        r -= 0.5 * f / r;
        f = r*r - n;
    }

    return r;
}

int main()
{
    double epsilon = .0000000001;
    double n = 2.0;

    printf("root_NR(%f) == %2.9f\n", n, root_NR(n, epsilon));
}