The error you get is because you don't actually 'do' anything, you only check.
>= means check if greater than, or equal to. It does not change j.
To inclement j you need to use something like below, depending on what you need to do.
j = j + 1;
j += 1;
j++;
j += n;
j *= n;
Hope this helps you on your way, if not, feel free to post a comment.