[Solved] Unity Doublejump in C#

Haven’t tested your code, but the following should work:

using UnityEngine;

public class PlatformerCharacter2D : MonoBehaviour 
{
    bool facingRight = true;                            // For determining which way the player is currently facing.

    [SerializeField] float maxSpeed = 10f;              // The fastest the player can travel in the x axis.
    [SerializeField] float jumpForce = 400f;            // Amount of force added when the player jumps. 

    [Range(0, 1)]
    [SerializeField] float crouchSpeed = .36f;          // Amount of maxSpeed applied to crouching movement. 1 = 100%

    [SerializeField] bool airControl = false;           // Whether or not a player can steer while jumping;
    [SerializeField] LayerMask whatIsGround;            // A mask determining what is ground to the character

    Transform groundCheck;                              // A position marking where to check if the player is grounded.
    float groundedRadius = .2f;                         // Radius of the overlap circle to determine if grounded
    bool grounded = false;                              // Whether or not the player is grounded.
    Transform ceilingCheck;                             // A position marking where to check for ceilings
    float ceilingRadius = .01f;                         // Radius of the overlap circle to determine if the player can stand up
    Animator anim;                                      // Reference to the player's animator component.

    int maxNumberOfAirJumps = 1;                        // Number of times the player can jump in the air
    int numberOfAirJumpsLeft = 0;


    void Awake()
    {
        // Setting up references.
        groundCheck = transform.Find("GroundCheck");
        ceilingCheck = transform.Find("CeilingCheck");
        anim = GetComponent<Animator>();
    }


    void FixedUpdate()
    {
        // The player is grounded if a circlecast to the groundcheck position hits anything designated as ground
        grounded = Physics2D.OverlapCircle(groundCheck.position, groundedRadius, whatIsGround);
        anim.SetBool("Ground", grounded);

        // Set the vertical animation
        anim.SetFloat("vSpeed", rigidbody2D.velocity.y);
    }


    public void Move(float move, bool crouch, bool jump)
    {    
        // If crouching, check to see if the character can stand up
        if(!crouch && anim.GetBool("Crouch"))
        {
            // If the character has a ceiling preventing them from standing up, keep them crouching
            if( Physics2D.OverlapCircle(ceilingCheck.position, ceilingRadius, whatIsGround))
                crouch = true;
        }

        // Set whether or not the character is crouching in the animator
        anim.SetBool("Crouch", crouch);

        //only control the player if grounded or airControl is turned on
        if(grounded || airControl)
        {
            // Reduce the speed if crouching by the crouchSpeed multiplier
            move = (crouch ? move * crouchSpeed : move);

            // The Speed animator parameter is set to the absolute value of the horizontal input.
            anim.SetFloat("Speed", Mathf.Abs(move));

            // Move the character
            rigidbody2D.velocity = new Vector2(move * maxSpeed, rigidbody2D.velocity.y);

            // If the input is moving the player right and the player is facing left...
            if(move > 0 && !facingRight)
                // ... flip the player.
                Flip();
            // Otherwise if the input is moving the player left and the player is facing right...
            else if(move < 0 && facingRight)
                // ... flip the player.
                Flip();
        }

        // If the player should jump...
        if (grounded && jump) {
            // Add a vertical force to the player.
            anim.SetBool ("Ground", false);
            rigidbody2D.AddForce (new Vector2 (0f, jumpForce));
            numberOfAirJumpsLeft = maxNumberOfAirJumps; //Reset the air jumps when the player jumps
        }
        else if (!grounded && jump && numberOfAirJumpsLeft  > 0)
        {
            rigidbody2D.AddForce (new Vector2 (0f, jumpForce));
            numberOfAirJumpsLeft--; //One less jump 
        }
    }


    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;
    }
}

also all the [SerializeField] are probably unnessacery