Variable not assigned but is.

using UnityEngine; using System.Collections;

public class MasterScript : MonoBehaviour { public GameObject zSOne; public GameObject zSTwo; public GameObject Zombie; public GameObject player; private int ZomsSpawned = 0; private int chosenSpawn; private int numberZombsPR = 1; private int numberZombsLeft = 1; private int currentRound = 1; private int points = 0; public GameObject[] spawners;

 // Use this for initialization
 void Start () {
     setSpawns ();
     currentRound = 1;
     numberZombsLeft = numberZombsPR;
 }

 public void setSpawns(){
     spawners = new GameObject[] {zSOne, zSTwo};
 }

 public void spawnZomb() {
     chosenSpawn = Random.Range (0, spawners.Length - 1);
     Vector3 spawner = new Vector3 (spawners[chosenSpawn].transform.position.x, spawners[chosenSpawn].transform.position.y, spawners[chosenSpawn].transform.position.z);
     Instantiate (Zombie, spawner, Quaternion.identity);
     ZomsSpawned += 1;

 }

 public int getCurrentRound () {
     return currentRound;
 }

 public void addPoints(int pointsGained) {
     points += pointsGained;
 }

 public int getZTR() {
     return numberZombsLeft;
 }

 public int calculateZombiesPR () {
     numberZombsPR = currentRound;
     return numberZombsPR;
 }

 public void changeRound() {
     currentRound += 1;
     calculateZombiesPR ();
     numberZombsLeft = numberZombsPR;
     ZomsSpawned = 0;
 }

 public int killZom() {
     return numberZombsLeft -= 1;
 }

 // Update is called once per frame
 void Update () {


     if (ZomsSpawned < numberZombsPR) {
         
         spawnZomb ();
     }

     if (numberZombsLeft == 0) {
         changeRound ();
     }

 }

 void OnGUI() {
     GUI.Box (new Rect(20, 20, 100, 20 ), currentRound.ToString());
     GUI.Box (new Rect(Screen.width - 100, Screen.height - 20, 100, 20 ), points.ToString());
     GUI.Box (new Rect(0, Screen.height - 20, 100, 20 ), numberZombsPR.ToString());
 }

}