C/C++ NaN constant (literal)?
c, c++, nan
Solution
In C, `NAN` is declared in `<math.h>`.
In C++, `std::numeric_limits<double>::quiet_NaN()` is declared in `<limits>`.
But for checking whether a value is NaN, you can't compare it with another NaN value. Instead use `isnan()` from `<math.h>` in C, or `std::isnan()` from `<cmath>` in C++.
Problem
Is this possible to assign a `NaN` to a `double` or `float` in C/C++? Like in JavaScript you do: `a = NaN`. So later you can check if the variable is a number or no.