Health won't update in GUI

Basically, I'm trying to make it so that this code updates my GUI to keep track of how much health the player and enemy has. Only problem is that it won't update the GUI, it just stays at 2. The print quotes output the correct health in the console, but not in the GUI. I've only attached this script to my CannonBall and my GUI Text file. Any help would be much appreciated.

var hpPlayer : int = 2;
var hpEnemy : int = 2;
var playerDead : boolean = false;
var enemyDead : boolean = false;
var x = 1;

function OnTriggerEnter(hit : Collider)
    if (collider.gameObject.tag == "CannonBall")

function OnCollisionEnter(collision : Collision){
   if(collision.gameObject.tag == "Player"){
       print("hit player " + hpPlayer);
       if (hpPlayer<=0) playerDead = true;

      if(collision.gameObject.tag == "Enemy"){
       print("hit enemy " + hpEnemy);
       if (hpEnemy<=0) enemyDead = true;

function OnGUI () {
    hpP = hpEnemy + "";
    GUI.Label (Rect (10, 10, 100, 20), "HP Player: " + (hpPlayer).ToString());
    GUI.Label (Rect (10, 30, 100, 20), "HP Enemy: "(hpEnemy).ToString());

Your trouble lies in the fact that this script is instantiated once for every GameObject it is attached to. The instance that is attached to your GUI has its own copy of the `hpPlayer` and `hpEnemy` variables, and since the GUI is never colliding with the player, these copies that are being displayed are never being modified.

Additionally, I'm assuming your using `Instantiate` on each of your cannon balls. Each of these will also have their own copy and you have the same problem.

The quick fix here is to declare those shared variables as `static`, that way there is only one copy that is shared between every instance of the script. Check out this explanation from the Script Reference.