Rotate a grid of points in C++

Question

If i had an array of point structs defined as

struct Point{

    float x;
    float y;

};

How would I rotate the points in this array by a given angle?

As an example:

Any help would be appreciated!

Answer 1

float x_old = p.x; float y_old = p.y;
p.x = x_old * cos(a) - y_old * sin(a);
p.y = x_old * sin(a) + y_old * cos(a);

Of course, if you are rotating many points by the same angle, you will want to save the sin & cos, instead of calculating them twice per point.