How to keep going forward while jumping ?

Hello, i'm trying so hard to make my character ( a cube ) keep going forward while jumping, but I just can't find a solution. I tried to put my even out of the .isGround if condition, but still doesn't work. Here is my code: ( sorry for the really bad organisation, i'm just trying to get part of codes from here and here, i'm learning from scratch ) using UnityEngine; using System.Collections;

 public class CubeMove : MonoBehaviour {
 
     public float speed = 7.0f;
     public float jumpSpeed = 6.0f;
     public float gravity = 5.0f;
 
     private Vector3 moveDirection = Vector3.zero;
     private CharacterController controller;
 
 
     // Use this for initialization
     void Start()
     {
         Cursor.visible = false;
         controller = GetComponent<CharacterController>();
     }
 
     // Update is called once per frame
     void Update()
     {
 
         if (controller.isGrounded) {
 
             if (Input.GetKey (KeyCode.Z)) {
                 transform.Translate (Vector3.forward * 11 * Time.deltaTime);
             }
 
             if (Input.GetKey (KeyCode.S)) {
                 transform.Translate (Vector3.back * 11 * Time.deltaTime);
             }
 
             if (Input.GetKey (KeyCode.Q)) {
                 transform.Rotate (-Vector3.up * 160 * Time.deltaTime);
             }
 
             if (Input.GetKey (KeyCode.D)) {
                 transform.Rotate (Vector3.up * 160 * Time.deltaTime);
             }
                 
         } else {}
 
         if (Input.GetButton ("Jump")) {
             moveDirection = Vector3.up * jumpSpeed;    
         }
 
         moveDirection.y -= gravity * Time.deltaTime;
         controller.Move(moveDirection * Time.deltaTime);
 
 
     }
 }