Move when pressed 'a' or 'd'

Hi there,

So I want to make an object rotate clockwise and counter clockwise…

I have a relative position in which the object moves around, but I don’t know how to do it only when you press ‘a’ and when you press ‘d’…
What I’m I doing wrong?
Here’s my code:

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour
{
	public Transform circle;
	public float speed = 40;
	
	void Start ()
	{
		
	}
	
	void Update ()
	{
		while(Input.GetButtonDown("a"))
			transform.RotateAround (circle.position, Vector3.left, speed * Time.deltaTime);

		while(Input.GetButtonDown("d"))
			transform.RotateAround (circle.position, Vector3.left, speed * Time.deltaTime);
	}
}

First of all, use GetButton instead of GetButtonDown as that only read when the moment you pressed it.