Finding verticies of a polygon given the number of sides? [closed] - c++

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I am trying to a function that will find all the vertices of a polygon given X number of sides and a radius r. My overall goal is to make a circle but since you can only draw straight lines I will have to make a polygon. So all of the polygons are going to be centred on the point (0,0). And I want to find all the coordinates for a polygon with 6 sides and radius that will iterate from .1 to 1.0. This should form a 10 circles inside of each other.
Here is what I have so far:
Here are my errors:
52:33: error: variable-sized object ‘vertices’ may not be initialized
57:17: error: request for member ‘insert’ in ‘vertices’, which is of non-class type ‘iPoint [(((long unsigned int)(((long int)nVertices) + -0x00000000000000001)) + 1)]’
My goal for the for loop is to get all the coordinates for a single polygon for the given radius and stick them in the verticies array as a 2 dimensional Point (x coordinate and a y coordinate).

Answer 1

I would take Point vertices[nVerticies] = {}; out of the loop (before the for). I would additionally correct verticies to vertices. Also, math functions sin and cos usually work in radians, not degrees. Finally, the angle increment can't be constant but depend (inversely) on nVertices.
Taking all together:
double radius = 0.1;
int nVertices = 6;
double angle = pi()*2/nVertices ;
while(radius <= 1.0)
{
iPoint vertices[nVertices];
for (int i = 0; i < nVertices; i++)
{
double x = 0 + radius * sin(i * angle);
double y = 0 + radius * cos(i * angle);
vertices[i]= iPoint(x,y) ;
}
radius = radius + 0.1;
}

Answer 2

Is there any advice?
The angular distance between two points on a regular flat 2D polygon is 2pi / N
Update due to comment
I'd write it slightly differently.
#include <math.h> // for M_PI
void circle_points(
double const radius,
int const n_points,
std::vector<Point<double>> &out_points )
{
out_points.resize(n_points);
double const angular_distance = M_PI / (double)n_points;
for( int i = 0; i < n_points; i++ ) {
double const x = radius * sin(i * angular_distance);
double const y = radius * cos(i * angular_distance);
out_points[i] = Point<double>(x,y);
}
}
void concentric_circles(
double const radius_start,
double const radius_end,
int const n_circles,
int const n_points_per_circle,
std::vector<std::vector<Point<double>> &out_circles )
{
out_circles.resize(n_circles);
double const radius_increment = (radius_end - radius_start) / n_circles;
for( int i = 0; i < n_circles; i++ ) {
circle_points(
radius_start + radius_increment*i,
n_points_per_circle,
out_circles[i] );
}
}
I'm passing the vectors by reference here to avoid deep copies when entering / leaving the function scopes.

Answer 3

If you would like vertices to be a static array and initialize it , declare 'nVertices' as a macro or const int.
const int nVertices = 6;