Double Jump

Hello Unity3D i have a problem with making my characters double jump.The problem is whenever i try to make my character double jump,At the start of the game the characters fall through the arena instead of double jumping.Is it because of the gravity or is it because i have to make a separate script in order for my characters to double jump?If anyone knows how i can fix this problem.Can you please tell me how?I have been stuck on this for a week....

 #pragma strict
 var Run:AudioClip;
 var rotationSpeed : float = 10;
 var walkSpeed : float = 7;
 var gravity : int = 50;
 var body : Transform;
 audio.volume = 0;
 private var double_jump : boolean = true;
 private var  yRot: float;
 private var moveDirection : Vector3 = Vector3.zero;
 function Update () {
     var Controller : CharacterController = GetComponent(CharacterController);
     var vertical : Vector3 = transform.TransformDirection(Vector3.forward);
     var horizontal : Vector3 = transform.TransformDirection(Vector3.right);
     var height : Vector3 = transform.TransformDirection(Vector3.up);
     var horizontal2: Vector3 = transform.TransformDirection(Vector3.left);
     if (Controller.isGrounded)    
     double_jump = true;{
     if(Input.GetKeyDown("space")){
     
         moveDirection.y -= gravity * Time.deltaTime;
         
         animation.Play("Jump");
         Jump();
         
 }
     
     
     
     if(Input.GetAxis("Vertical")||Input.GetAxis("Horizontal")){
         if (!animation.IsPlaying("Jump"))
             if (!animation.IsPlaying("Jump"))
         if(!animation.IsPlaying("Kick1"))
     if(!animation.IsPlaying("Sword_5"))
     if(!animation.IsPlaying("Sword_6"))
     if(!animation.IsPlaying("Sword_7"))
     if(!animation.IsPlaying("Sword_8"))
     if(!animation.IsPlaying("Spinning_Slashes"))
         animation.CrossFade("Run2");
         animation["Run2"].speed = walkSpeed/100;
         
         Controller.Move((vertical * (walkSpeed * Input.GetAxis("Vertical"))) * Time.deltaTime);
         Controller.Move((horizontal * (walkSpeed * Input.GetAxis("Horizontal"))) * Time.deltaTime);
         audio.Play();
 }else{
     if (!animation.IsPlaying("Jump"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_5"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_6"))
     if(!animation.IsPlaying("Overhead_slash4"))
     if(!animation.IsPlaying("Overhead_slash3"))
     if(!animation.IsPlaying("Violets_Pause_2"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_1"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_2"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_3"))
     if(!animation.IsPlaying("Assassin_s_Greeting_Part_4"))
     if(!animation.IsPlaying("punch1"))
     if(!animation.IsPlaying("punch2"))
     if(!animation.IsPlaying("punch3"))
     if(!animation.IsPlaying("punch4"))
     if(!animation.IsPlaying("punch5"))
     if(!animation.IsPlaying("Berserk"))
     if(!animation.IsPlaying("Teleport"))
     if(!animation.IsPlaying("Snake_"))
     if(!animation.IsPlaying("Snake__2"))
     if(!animation.IsPlaying("Snake__3"))
     if(!animation.IsPlaying("Snake__4"))
     if(!animation.IsPlaying("Snake__Launcher"))
     if(!animation.IsPlaying("Juggle_Launcher_Ground"))
     if(!animation.IsPlaying("invisibility"))
     if(!animation.IsPlaying("Violet_Poison_Dagger_Throw"))
     if(!animation.IsPlaying("Demonic_Wave"))
     if(!animation.IsPlaying("Slash_Combo"))
     if(!animation.IsPlaying("Slash_Combo_2"))
     if(!animation.IsPlaying("Rex_Pause"))
     if(!animation.IsPlaying("Escalibur"))
     if(!animation.IsPlaying("Invisibility"))
     if(!animation.IsPlaying("Rex_Sword_Combo"))
     animation.CrossFade("Stance");
 else{
 
     if (Input.GetButtonDown("space"))
     {
         
         moveDirection.y -= gravity * Time.deltaTime;        
                     
         double_jump = false;
         
     }
 }        
 
 
     Controller.Move((vertical * (walkSpeed * Input.GetAxis("Vertical"))) * Time.deltaTime);
     Controller.Move((horizontal * (walkSpeed * Input.GetAxis("Horizontal"))) * Time.deltaTime);
     audio.Play();
     
 
     }
     
 
     if(Input.GetAxis("Vertical")){
         yRot += 10* Input.GetAxis("vertical");
     }
         
    }
 }    
 function LateUpdate(){
   // Rotate the Character to match the direction he/she is going
   if(Input.GetAxis("Vertical") == 0){
     if(Input.GetAxis("Horizontal") > 0){
       body.localEulerAngles.y = 90;//Right sideways running
     }else if(Input.GetAxis("Horizontal") < 0){
       body.localEulerAngles.y = 270;//Left sideways running
 
       
     }
   }else if(Input.GetAxis("Vertical") > 0){
     if(Input.GetAxis("Horizontal") > 0){
       body.localEulerAngles.y = -270;
     }else if(Input.GetAxis("Horizontal") < 0){
       body.localEulerAngles.y = -90;
     }
   }else if(Input.GetAxis("Vertical") < 0){
     if(Input.GetAxis("Horizontal") == 0){
       body.localEulerAngles.y = -180;
     }else if(Input.GetAxis("Horizontal") > 0){
       body.localEulerAngles.y = -180;
     }else if(Input.GetAxis("Horizontal") < 0){
       body.localEulerAngles.y = -180;
     }
   }
 }
 function Jump(){
     gravity = 30;
     yield WaitForSeconds(0.2);
     gravity = -50;
 }