My codes working correctly in game scene but when I try build I am getting some errors ?

My codes working in game scene but when I try build (android and pc) I am getting errors. If I take the codes comment line, it is building. Where is my mistake?

Code (CSharp):

1.   if(GameObject.Find("EasyMode"))
2.         {
3.  
4.             if(timer>=1800)
5.             {
6.                 var yesno = UnityEditor.EditorUtility.DisplayDialog("OYUN BİTTİ", "Yeniden başlamak ister misiniz? ", "Yes", "No");
7.                 if(yesno == true)
8.                 {
9.                     Application.LoadLevel("StartMenu");
10.                 }
11.                 else
12.                 {
13.                     Application.Quit();
14.                 }
15.                 }
16.             }
17.         else if(GameObject.Find("NormalMode"))
18.         {
19.             if(timer>=1500)
20.             {
21.                 var yesno = UnityEditor.EditorUtility.DisplayDialog("OYUN BİTTİ", "Yeniden başlamak ister misiniz?", "Yes", "No");
22.                 if(yesno == true)
23.                 {
24.                     Application.LoadLevel("StartMenu");
25.                 }
26.                 else
27.                 {
28.                     Application.Quit();
29.                 }
30.             }
31.         }
32.  
33.         else if(GameObject.Find("HardMode"))
34.         {
35.  
36.         if(timer>=5)
37.         {
38.             var yesno = UnityEditor.EditorUtility.DisplayDialog("OYUN BİTTİ", " Yeniden başlamak ister misiniz? ", "Yes", "No");
39.             if(yesno == true)
40.             {
41.                 Application.LoadLevel("StartMenu");
42.             }
43.             else
44.             {
45.                 Application.Quit();
46.             }
47.         }
48.         }

 

The UnityEditor namespace is only available in the editor. It's used for editor controls (making the game), and cannot be used in the gameplay.

For game dialogue, either use the old GUI system, or learn the canvas system introduced more recently.

 

Can you show me a little sample? how will I write gameplay dialog?

 

https://unity3d.com/learn/tutorials/topics/user-interface-ui