#ifndef _USE_MATH_DEFINES
#   error "Define _USE_MATH_DEFINES in the build settings, please."
#   include <fatal-error>   // Just stop the compiler here.
#endif
#include <math.h>

const double pi = M_PI;

template< auto unitfunc() -> double >
struct Angle_
{
    double value;

    operator double() const { return value; }

    static auto unit() -> double { return unitfunc(); }

    template< class Other_angle_type >
    auto to_() const
        -> Other_angle_type
    { return {(value / unit()) * Other_angle_type::unit()}; }
};

auto degrees_unit() -> double { return 180; }
using Degrees = Angle_<degrees_unit>;

auto radians_unit() -> double { return pi; }
using Radians = Angle_<radians_unit>;

#include <iomanip>
#include <iostream>
using   std::setprecision,
        std::cout, std::endl, std::fixed;

auto main()
    -> int
{
    const Radians r = Degrees{ 180 }.to_<Radians>();

    cout << sin( r ) << endl;
    cout << cos( r ) << endl;
    cout << endl;
    cout << fixed << setprecision( 10 );
    cout << sin( r ) << endl;
    cout << cos( r ) << endl;
}