graphics - Trouble drawing star with an even number of points with turtle in Java -


alright, assignment, , have close figured out. basically, given code create turtle , test client draws polygon n sides. instructions modify test client draws star n points. odd-numbered values of n easy because made change turtle.turnleft(angle) turtle.turnleft(angle*2).

i think of trouble coming complete ignorance of star geometry. tried draw out , kind of make triangles between points, , i've tested few different things, keep getting lines resemble this: vvvv , turn left.

original code:

public class turtle { private double x, y; private double angle;  public turtle(double x0, double y0, double a0) { x=x0; y=y0; angle=a0;}  public void turnleft(double delta) {angle += delta;}  public void goforward(double step) {     double oldx=x, oldy=y;     x+=step*math.cos(math.toradians(angle));     y+=step*math.sin(math.toradians(angle));     stddraw.line(oldx, oldy, x, y); }  public static void main(string[] args) {     int n=integer.parseint(args[0]);     double angle = 360.0/n;     double step = math.sin(math.toradians(angle/2));      turtle turtle= new turtle(0.5, 0.0, angle/2);      (int i=0;i<n;i++)     {         turtle.goforward(step);         turtle.turnleft(angle); }}}

edited again:

revised code (again):

  public static void main(string[] args) {     int n=integer.parseint(args[0]);     double angle = 360.0/n;      double q = ((n-2)*180)/n;     double p = ((180-q)/2);     double t = (180-q);     double v = (180 - 2*t);      double step = math.sin(math.toradians(angle/2));       turtle turtle= new turtle(0.5, 0.0, (angle/2 + p));      (int i=0;i<n;i++)     {           turtle.goforward(step/2);         turtle.turnleft(-t);         turtle.goforward(step/2);         turtle.turnleft(180-v); }}}

this 1 gives perfect star values of n except 7 reason.

enter image description here

enter image description here

enter image description here

double q = ((n-2)*180.)/n;

this ensure whole expression computed using doubles , avoid truncation of decimal part... (not problem n=3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20...).


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