Hello .. I want to create a polygon class with variable number of corners. The problem is in line 3 of the code. I can't use "fl_corners", which is the number of corners of the polygon, before it is defined.

I hope somebody can help me with this problem.

class Fl
{
 PVector [] vertices = new PVector[fl_corners];
 float w;
 float angle;
 int fl_corners;

 
 Fl (int fl_corners_, float w_)
 {
   fl_corners = fl_corners_;
   w = w_;
   angle = 360/fl_corners;
 
     
   for (int i=0; i<fl_corners; i++)
   {
     vertices[i] = new PVector((w/2)*cos(radians(angle)), (w/2)*sin(radians(angle)));    
   }
 }
   
 void create()
 {
   beginShape();
   for (int i=0; i<fl_corners; i++)
   {
     vertex(vertices[i].x, vertices[i].y);
   }
   endShape();
 }
 
}

Well - clearly you can't create the array before you know how long it's going to be, but you do at least need to declare its existence:

Code:

class Fl {

 float w;
 float angle;
 int fl_corners;
 PVector [] vertices;
 
 Fl (int fl_corners_, float w_) {
   fl_corners = fl_corners_;
   vertices = new PVector[fl_corners];
   w = w_;
   angle = 360/fl_corners;
 
     
   for (int i=0; i<fl_corners; i++)
   {
     vertices[i] = new PVector((w/2)*cos(radians(angle)), (w/2)*sin(radians(angle)));    
   }
 }
   
 void create()
 {
   beginShape();
   for (int i=0; i<fl_corners; i++)
   {
     vertex(vertices[i].x, vertices[i].y);
   }
   endShape();
 }
 
}  

A couple of minor points on coding style:

1.  What's an 'Fl'?  If you're going to create a class you need to give it a meaningful name so people know what they're going to use it for

2. I find all those underscores in the argument names really ugly and actually a little difficult to read.  It's a matter of taste, but you can use the same name as the variable for the argument in a constructor and precede the Object variable with 'this' - e.g.:

Code:

class myPolygonClass {

 float w;
 float angle;
 int corners;
 PVector [] vertices;
 
 myPolygonClass (int corners, float w) {
   this.corners = corners;
   this.vertices = new PVector[corners];
   this.w = w;
   this.angle = 360/corners;
 
     
   for (int i=0; i<corners; i++)   {
     vertices[i] = new PVector((w/2)*cos(radians(angle)), (w/2)*sin(radians(angle)));
     println(vertices[i].x + " " + vertices[i].y);
   }
 } 

Note that I've added a println to highlight a slight problem - you might want to use the value of i to adjust those vertex coordinates.  I'd also be tempted to add parameters to the create method so you can choose where to place your rendered polygon...

Quote:


Whilst separating this out from the PVector creation is neater and easier to read, you do still have to create the PVector object first:

Code:

for (int i=0; i<corners; i++) {
        vertices[i] = new PVector(); // create a PVector object!
	vertices[i].x = 1;//(w/2)*cos(radians(angle*i));
	vertices[i].y = (w/2)*sin(radians(angle*i));   
    }