Double jump 2D Platformer

I did a platformer game and i using the character and cript from Unity 2D Platformer game but i couldn't double jump function. I tried adding but it was not. Can you help me for this fucntion i will give the script.

 using UnityEngine;
 using System.Collections;
 using TouchControlsKit;
 
 public class PlayerControl : MonoBehaviour
 {
     [HideInInspector]
     public bool facingRight = true;            // For determining which way the player is currently facing.
     [HideInInspector]
     public bool jump = false;                // Condition for whether the player should jump.
     [HideInInspector]
     public bool grounded = false;            // Whether or not the player is grounded.
     static bool GetButtonDown;
     public float moveForce = 365f;            // Amount of force added to move the player left and right.
     public float maxSpeed = 5f;                // The fastest the player can travel in the x axis.
     public AudioClip[] jumpClips;            // Array of clips for when the player jumps.
     public float jumpForce = 1000f;            // Amount of force added when the player jumps.
     private Transform groundCheck;            // A position marking where to check if the player is grounded.
     private Animator anim;                    // Reference to the player's animator component.
 
     bool doubleJump = false;
 
 
     void Awake()
     {
         // Setting up references.
         groundCheck = transform.Find("groundCheck");
         anim = GetComponent<Animator>();
 
     }
 
 
     void Update()
     {
         // The player is grounded if a linecast to the groundcheck position hits anything on the ground layer.
         grounded = Physics2D.Linecast(transform.position, groundCheck.position, 1 << LayerMask.NameToLayer("Ground"));
 
         // If the jump button is pressed and the player is grounded then the player should jump.
         if(InputManager.GetButtonDown("Button0") && grounded || !doubleJump)
             jump = true;
 
     }
 
 
     void FixedUpdate ()
     {
         // Cache the horizontal input.
         float h = InputManager.GetAxis("DPad0", "Horizontal");
         h = Mathf.Clamp( h, -1f, 1f );
 
         // The Speed animator parameter is set to the absolute value of the horizontal input.
         anim.SetFloat("Speed", Mathf.Abs(h));
 
         // If the player is changing direction (h has a different sign to velocity.x) or hasn't reached maxSpeed yet...
         if(h * GetComponent<Rigidbody2D>().velocity.x < maxSpeed)
             // ... add a force to the player.
             GetComponent<Rigidbody2D>().AddForce(Vector2.right * h * moveForce);
 
         // If the player's horizontal velocity is greater than the maxSpeed...
         if(Mathf.Abs(GetComponent<Rigidbody2D>().velocity.x) > maxSpeed)
             // ... set the player's velocity to the maxSpeed in the x axis.
             GetComponent<Rigidbody2D>().velocity = new Vector2(Mathf.Sign(GetComponent<Rigidbody2D>().velocity.x) * maxSpeed, GetComponent<Rigidbody2D>().velocity.y);
 
         // If the input is moving the player right and the player is facing left...
         if(h > 0 && !facingRight)
             // ... flip the player.
             Flip();
         // Otherwise if the input is moving the player left and the player is facing right...
         else if(h < 0 && facingRight)
             // ... flip the player.
             Flip();
 
         // If the player should jump...
         if(jump)
         {
             // Set the Jump animator trigger parameter.
             anim.SetTrigger("Jump");
 
             // Play a random jump audio clip.
             int i = Random.Range(0, jumpClips.Length);
             AudioSource.PlayClipAtPoint(jumpClips[i], transform.position);
 
 
             // Add a vertical force to the player.
             GetComponent<Rigidbody2D>().AddForce(new Vector2(0f, jumpForce * 1.5f));
 
             // Make sure the player can't jump again until the jump conditions from Update are satisfied.
             jump = false;
         }
     }
     
     
     public void Flip ()
     {
         // Switch the way the player is labelled as facing.
         facingRight = !facingRight;
 
         // Multiply the player's x local scale by -1.
         Vector3 theScale = transform.localScale;
         theScale.x *= -1;
         transform.localScale = theScale;
     }
 }