The following code example is taken from the book
Object-Oriented Programming in C++
by Nicolai M. Josuttis, Wiley, 2002
© Copyright Nicolai M. Josuttis 2002
#include <iostream>
#include <cmath>
#include "frac.hpp"
int main()
{
CPPBook::Fraction x(1,4);
//...
std::cout << std::sqrt(x.toDouble()) // output root of x as a double
<< std::endl;
}