#include <cmath>
#include <iostream>

double const pi = 4 * std::atan(1.0);
char const* const zweck = "Umrechnung kartesisch => polar";

struct Punkt2D
{
  double x, y;
  double abstand() const { return std::sqrt(x*x+y*y); }
  double winkel()  const { return std::atan2(y, x); }
};

int main()
{
  Punkt2D const p = {3, 4};

  std::cout 
    << zweck << '\n';
    << "x=" << p.x << " y=" << p.y << '\n'
    << "r=" << p.abstand() 
    << " phi=" << p.winkel()*180/pi << " Grad" << '\n';
}