Unity will not run when I assign an animation to a keystroke

Hi all,

I am running Unity 4.3.1f1 on a 2013 MacBookPro with OS X 10.9.3.

So, I am trying to create an animation using scripting.

This is my current code: using UnityEngine; using System.Collections;

 public class HorseAnim : MonoBehaviour {
 
     public Sprite[] spritesRight;
     public Sprite[] spritesIdle;
     public float framesPerSecond;
     private SpriteRenderer spriteRendererRight;
 
 
     // Use this for initialization
     void Start () {
         spriteRendererRight  = renderer as SpriteRenderer;
 
     }
     
     // Update is called once per frame
     void Update () {
     
         int index = (int)(Time.timeSinceLevelLoad * framesPerSecond);
         index = index % spritesRight.Length;
         spriteRendererRight.sprite = spritesRight[ index ];
         }
     }

When I run Unity using this code, my actor defaults to the animation within no matter what state it is in. When I try to add a keystroke like this:

 using UnityEngine;
 using System.Collections;
 
 public class HorseAnim : MonoBehaviour {
 
     public Sprite[] spritesRight;
     public Sprite[] spritesIdle;
     public float framesPerSecond;
     private SpriteRenderer spriteRendererRight;
 
 
     // Use this for initialization
     void Start () {
         spriteRendererRight  = renderer as SpriteRenderer;
 
     }
     
     // Update is called once per frame
     void Update () {
         while(Input.GetButtonDown("Horizontal"))
         {
         int index = (int)(Time.timeSinceLevelLoad * framesPerSecond);
         index = index % spritesRight.Length;
         spriteRendererRight.sprite = spritesRight[ index ];
         }
     }
 }

and then preview the scene in Unity, Unity will preview it for a second, but then it will stall, and the spinning pinwheel of doom will appear. I cannot do anything during this period, the game will not run, and I eventually have to force-quit Unity.

Why is Unity crashing when I add that keystroke?

When I try using "if", the actor changes its image only once when I press the button, and I have to release it and press it again for the actor to move to the next frame.