Object reference not set to an instance of an object

i was working in project space shooter which is available in unity website .in video no 14-counting points .i got stuck .i'm getting an error on destroyByContact script .it says "Object reference not set to an instance of an object".here is my 'Destroy By Contact' Script and 'Game Controller' script.

DestroyByContact.cs

Code (CSharp):

1.  
2. using UnityEngine;
3. using System.Collections;
4.  
5. public class DestoryByContact : MonoBehaviour {
6.     public GameObject explosion;
7.     public GameObject playerexplosion;
8.     public int scorevalue;
9.     private GameController gamecontroller;
10.  
11.     void start()
12.     {
13.  
14.         GameObject gamecontrollerobject = GameObject.FindWithTag ("GameController");
15.         if (gamecontrollerobject != null)
16.         {
17.             gamecontroller=gamecontrollerobject.GetComponent <GameController>();
18.         }
19.         if (gamecontroller== null)
20.         {
21.             Debug.Log("can.t find game controller");      
22.         }
23.     }
24.  
25.     void OnTriggerEnter( Collider other)
26.     {
27.         if (other.tag == "Boundary")
28.                {
29.             return;      
30.                  }
31.         Instantiate (explosion,transform.position,transform.rotation);
32.         if (other.tag == "Player")
33.                   {
34.                         Instantiate (playerexplosion, other.transform.position, other.transform.rotation);
35.                 }
36.         gamecontroller.AddScore (scorevalue);
37.  
38.         Destroy (other.gameObject);
39.         Destroy (gameObject);
40.  
41.     }
42.  
43. }
44.  

GameController.cs

Code (CSharp):

1.  
2.  
3. using UnityEngine;
4. using System.Collections;
5.  
6. public class GameController : MonoBehaviour {
7.     public GameObject hazard;
8.     public Vector3 spawnvalues;
9.     public int hazardcount;
10.     public float spanwait;
11.     public float startwait;
12.     public float wavewait;
13.     public GUIText scoreText;
14.     private int score;
15.     // Use this for initialization
16.     void Start () {
17.          score = 0;
18.         updateScore ();
19.         StartCoroutine(spawnWave ());
20.    
21.     }
22.     IEnumerator spawnWave()
23.     {
24.         yield return new WaitForSeconds (startwait);
25.         while (true) {
26.                         for (int i=0; i< hazardcount; i++) {
27.                                 Vector3 spawnPosition = new Vector3 (Random.Range (-spawnvalues.x, spawnvalues.x), spawnvalues.y, spawnvalues.z);
28.                                 Quaternion spanrotation = Quaternion.identity;
29.                                 Instantiate (hazard, spawnPosition, spanrotation);
30.                                 yield return new WaitForSeconds (spanwait);
31.                         }
32.             yield return new WaitForSeconds (wavewait);
33.                 }
34.  
35.     }
36.     public void AddScore(int newScorevalues)
37.     {
38.         score += newScorevalues;
39.         updateScore ();
40.         }
41.     void updateScore()
42.     {
43.         scoreText.text = "Score :" + score;
44.     }
45.  
46. }
47.  

Any Help Would Be Appreciated.
Thanks

 

Which line causes an error?

 

line no--36 in DestroyByContact.cs

 

Did you set scoreValue in unity?

 

yes

 

That means, game controller could not be initialized. You most likely got the message

in you console

 

Check this lines

Code (csharp):

1.  GameObject gamecontrollerobject = GameObject.FindWithTag ("GameController");
2.   gamecontroller=gamecontrollerobject.GetComponent <GameController>();
3.  

Possible problem might appears if your tag have a mistake or GameController contains in other namespace, if so you have to use "using namespace_with_GameController"

 

in this line i got the error message in runtime(play mode)

Code (CSharp):

1.    gamecontroller.AddScore (scorevalue);
2.      

after this line the next code

Code (CSharp):

1.         Destroy (other.gameObject);
2.         Destroy (gameObject);
3.  

doesn't work and my tag name is fine

 

Looks like you destroing your object with script and for now your gameObject == null

And I'm not sure that I'm fully understand you. You said that error caused by this

Which means this lines

wont run.
Or they are runs once, and after destroying your object you're recieving an error

 

Line 11:

Code (csharp):

1. void start()

is supposed to be

Code (csharp):

1. void Start()

The s has to be an uppercase character! Otherwise the start method is not executed by Unity.

 

yes you were right the 's' of start must be capital.

you just save my day.
thanks