Rotating a point around the origin in cpp?

Question

I want to rotate a point around the origin but I keep getting errors. The mathematical part is solid but the code seems to fail when I want it to update the x and y values from the specific points. Can you guys help me?

Kind regards, Vincent

#include <cmath>
#include <iostream>
#include <iomanip>


class Point
{
public:

    double x, y;
    // constructors

    Point()
        : x(0), y(0)
    {} 

    Point(double X, double Y)
        : x(X), y(Y)
    {}

    double roa(double angle) 
    { 
        double new_x = x*cos(angle) - y*sin(angle);
        double new_y = x*sin(angle) + y*sin(angle);
        x = new_x;
        y = new_y;

        return Point(x,y);
    }
};

int main()
{
    Point a(2,2); 
    a = a.roa(50);
    std::cout << a << std::endl;

    return 0
}

Solved! Thx for your help guys. You can find the new code below:

#include <cmath>
#include <iostream>
#include <iomanip>


class Point
{
public:

    double x, y;
    // constructors

    Point()
        : x(0), y(0)
    {} 

    Point(double X, double Y)
        : x(X), y(Y)
    {}

    Point roa(double angle) 
    {
        double angle_rad = angle / (180/M_PI);

        double new_x = x*cos(angle_rad) - y*sin(angle_rad);
        double new_y = x*sin(angle_rad) + y*cos(angle_rad);

        double x = new_x;
        double y = new_y;

        Point p;
        p.x = new_x;
        p.y = new_y;

        return p;

    }
};

int main()
{
    Point a(2,2); 
    a = a.roa(360);
    std::cout << a << std::endl;

    return 0
}

Answer 1

A few issues in the code. You are returning Point(x, y) on roa() while the function returns a double which makes it unable to compile. If you want to rotate the same point, you are already setting x and y values in roa(), no need to reassign the whole variable at a = a.roa(50) . Just do a.roa() with roa() modified as follows:

void roa(double angle) 
{ 
  double new_x = x*cos(angle) - y*sin(angle);
  double new_y = x*sin(angle) + y*cos(angle); // mistake here as well
  x = new_x;
  y = new_y;
}

Finally, as bialy pointed out, the angle should be in radians not degrees!

Answer 2

Documentation says that angle is in radians: http://www.cplusplus.com/reference/cmath/cos/

To convert angles to radians just

double angle_radians = angle_degrees / (180.0 / M_PI);