Putting changing differences in arrays

[gk9]

Hey all,

I'm trying to set up a simulation of orbit, and to find the way the forces work I need to find delta x and delta y for each planet in relation to all the others. I've set up arrays for x and y coordinates of the planets, but I'm having trouble finding a way to set up a loop that compares each x with each y and putting it into the result into an array that I can read from in an order that makes sense. So far, this is what I have:

where N = number of planets

  int i = 0; int j = 0; int counter = 0;
       
      while (j < N){
       if (i != j){
             deltax[counter] = px[j] - px[i];
             deltay[counter] = py[j] - py[i];
             counter++;
           }
             i++;
       if (i == N){
             j++; 
             i = 0;
           }
       }

I'm sure theres oodles of problems with this, and any help is appreciated. It's one of those problems where as a human I can say "well just compare this and those" but when it comes to putting it into code I'm lost!
Any help would be appreciated.