optional.cpp

/*

In the code below, modify the function `mysqrt` below so that it returns
an `std::optional<double>` rather than a double, and the program prints
`nothing` rather than `nan` for the call with `-10`. It will also require
to modify `square`.

*/

#include <cmath>
#include <iostream>
#include <optional>

double mysqrt(double d) // TO BE MODIFIED
{
  return std::sqrt(d);  // TO BE MODIFIED
}

double square(double d) // TO BE MODIFIED
{
  return d * d;         // TO BE MODIFIED
}

template <typename A>
std::ostream &operator<<(std::ostream &os, std::optional<A> const &opt) {
  if (opt) {
    return os << opt.value();
  } else {
    return os << "nothing";
  }
}

int main() {
  std::cout << square(mysqrt(10)) << std::endl;
  std::cout << square(mysqrt(-10)) << std::endl;
}