Cannot convert from void to PVector in Processing - processing

Question

I'm learning processing and am trying generate fractals using Pascal's triangle. This requires arrays of PVectors. I have run into an issue that I don't understand—I'm getting cannot convert from void to PVector
This is an excerpt, not every variable is defined in the excerpt, but I figure the issue is probably something such that I won't need to reveal more code than this—more code shown might just obfuscate the problem.
arrayCopy(points,old_points);
points = new PVector[int(pow(2, j))];
if (j == 1)
{
points[0] = new PVector(0,0);
}
if (j == 2)
{
points[0] = new PVector(1,0);
points[1] = new PVector(-1,0);
}
else
{
//j will be 3 for the THIRD term in the series
int number_of_terms_to_fill = int(pow(j - 1, 2));
int[] pasc = PascalTriangle(j - 1);
float real = findReal(pasc, x, y, number_of_terms_to_fill);
float imagi = findImagi(pasc, x, y, number_of_terms_to_fill);
PVector v = new PVector(real, imagi);
for (int k = 0; k < number_of_terms_to_fill; k = k + 2)
{
points[k] = old_points[k].add(v); //!!***PROBLEM LINE***!!!
points[k+1] = old_points[k].sub(v);
}
}
My other functions, such as findReal and findImagi, I believe are correct. The addition on the problem line should be an addition between two PVectors—a legal operation. Instead something is void? Perhaps arrayCopy isn't a deep copy like I'd want?
Not sure what is going on.

Answer 1

The method .add() does not return a PVector (it returns nothing, thus void) so you can't do
points[k] = old_points[k].add(v);
I suppose what you are trying to do is add v to old_points[k] and pass it to points[k] which will not work like that... You have to do it like this:
old_points[k].add(v);
points[k] = old_points[k];
old_points[k].sub(v);
points[k+1] = old_points[k];
In order for what you wrote to be valid, the add function should have been like this:
PVector add(PVector v) {
this.x += v.x;
this.y += v.y;
this.z += v.z;
return this;
}
Instead it looks sort of like this:
void add(PVector v) {
this.x += v.x;
this.y += v.y;
this.z += v.z;
}
Edit: After Ryan's comment below, I provide here another way, using the static .add() method which does return a PVector...
points[k] = PVector.add(old_points[k],v);
points[k+1] = PVector.sub(old_points[k],v);