Rotating a object towards a direction then move it

Hi normally just searching the forums / unity docs or googling around can solve my programming issues but i've been stuck for about the last month and i'm on the fourth attempt at making a basic tank controller with each attempt i'm getting closer and closer but right now I am just stuck.

My problem isn't with moving it but making it rotate towards the direction the player whats to travel then moving. I provided two videos to show what im trying to accomplish

What I want http://youtu.be/9zrxS0LcnRo

What I currently have http://youtu.be/8FSPA7863-c

Currently it rotates but doesn't stop when it faces forward and so and endless rotation occurs until you stop pressing forward

 public class attempt4 : MonoBehaviour 
 {
     
     Quaternion qtarget;    //quartnon target ie rotation
     public Transform waypoint; //the cube in front of the tank
     public Transform Turrent_pos;    //the top turrent of the tank
     public float rspeed = 10;    //turn speed of tank
     
     public float speed = 8;    //forward speed
 
     public bool tankBody = false;
     
     void LateUpdate() 
     {
         //Quaternion deltaRotation = Quaternion.Euler(waypoint.transform.position-transform.position);
         //rigidbody.MoveRotation(Quaternion.Slerp(rigidbody.rotation, deltaRotation, rspeed * Time.deltaTime));
 
         qtarget = Quaternion.LookRotation(waypoint.transform.position-transform.position);    //non ridgid body quatornon
 
         
         // based on input, determine requested action
         if (Input.GetAxis("Vertical") > 0) 
         { 
             // requesting forward
             transform.rotation = Quaternion.Slerp(transform.rotation, qtarget, rspeed * Time.deltaTime);    //this rotates the object towards the waypoint(direction camera is facing)
 
             transform.position+= (transform.TransformDirection(Vector3.forward) * speed * Time.deltaTime);    //this rotates the object to the direction we need to travel multiply by speed, progressed by time    
         } 
         else if (Input.GetAxis("Vertical") < 0) 
         {
             // requesting reverse
             transform.rotation = Quaternion.Slerp(transform.rotation, qtarget, rspeed * Time.deltaTime);
             
             transform.position-= (transform.TransformDirection(Vector3.forward) * speed * Time.deltaTime);
             
         }
     }
 }