I'm debating with a friend whether a ranger can add feats from his combat style only when he has to pick a combat style feat (and as such ignoring the prerequisites).
He keeps saying he read (in the APG)the ranger can choose those feats even at char level feat choices (lvl 1,3,5 etc,) so out of combat style pick, and still ignoring prerequisites.
What the other two have said.
And I doubt there's a ruling in the APG considering Ranger is a CRB class, and if anything, it would mention there... But it doesn't.
Your friend is engaging in some wishful thinking.
Your friend is wrong, except there is one feat in the natural attack style that specifically says rangers w/ that style can ignore the pre-reqs even when obtaining it as a general feat and not a bonus feat.
EDIT: Aspect of the Beast.
"A ranger who selects the natural weapon combat style can take this feat without having to meet the prerequisites (even if he does not select Aspect of the Beast as a bonus feat)."
There's only one example I know of like that, the Aspect of the Wild feat from the APG. It specifies that a ranger with the natural combat style can ignore its prereqs even when not using a combat style bonus feat.
And the fact that these feats specifically mention the exception to the rule strongly suggests that the rule is indeed that you cannot select combat style feats with your general slot unless you meet the prerequisite, or no exception notation would be necessary.
I also think he was referring to the Aspect of the beast feat, but i'm no ranger expert, i don't usually read about them.