How would I go about making space do nothing if I am in the air already?

Unity Engine
, ,
1 
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Jump : MonoBehaviour
{
    public CharacterController cc;
    public float gravity = -9.81f;
    public float gravityScale = 1;
    public float jumpHeight = 4;
    public float groundDistance = 0.4f;

    Vector3 velocity;

    public Transform groundCheck;

    public LayerMask groundMask;

    bool isGrounded;

    void Update()
    {

        isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

        if(isGrounded && velocity.y < 0)
        {
            velocity.y = -2f;
        }
       
        if (Input.GetKeyDown(KeyCode.Space))
        {
            velocity.y = Mathf.Sqrt(jumpHeight * -2f * (gravity * gravityScale));
        }
        velocity.y += gravity * gravityScale * Time.deltaTime;
        MovePlayer();
    }
    void MovePlayer()
    {
        cc.Move(new Vector3(0, velocity.y, 0) * Time.deltaTime);
    }

}
2 
if(!isGrounded && velocity.y > 0)
{
    if (Input.GetKeyDown(KeyCode.Space))
       {
             velocity.y = 0f;
        }
}

Something kind of like that.