Why does my slide out menu not work when i translate from JS to C#?

So I am practesing my translation and i decided to make a slide script in JS and it works like it should, so i started with the translation but I am having a problem in the sliding function itself it won't do it. My JS script:

 var MyBoxLeft = -200.0;
 
 var icon : Texture; var icon2 : Texture; var blankSkin : GUISkin;
 
 function OnGUI () { GUI.skin = blankSkin; var tBoxRect = new Rect(MyBoxLeft, 20.0, 220, 720); var tButtonRect = new Rect(MyBoxLeft, 160.0, 120, 30); var tBoxArt = new Rect(MyBoxLeft, 200.0, 120, 120);
 
 GUI.Box(tBoxRect, icon); GUI.Button(tButtonRect, "Click"); GUI.Box(tBoxArt, icon2); }
 
 function Update () {
 
 if (Input.GetKeyDown("space")) { AnimateBox(); }
 
 }
 
 function AnimateBox () {
 
 if (MyBoxLeft == -200.0) {
 
     while (MyBoxLeft < 20.0) {
     MyBoxLeft+=5.0;
     yield;
     }
 
 } else if (MyBoxLeft == 20.0) {
 
     while (MyBoxLeft > -200.0) {
     MyBoxLeft-=5.0;
     yield;
     }
 
 }
 
 }

and here is the C# script i have made:

 using UnityEngine;
 using System.Collections;
 
 public class GUI_Script : MonoBehaviour
 {
 
     float MyBoxLeft = -200f;
 
     public Texture icon;
     public Texture icon2;
     public GUISkin blankSkin;
 
     void OnGUI()
     {
         GUI.skin = blankSkin; 
         Rect tBoxRect = new Rect(MyBoxLeft, 20.0f, 220, 720);
         Rect tButtonRect = new Rect(MyBoxLeft, 160.0f, 120, 30);
         Rect tBoxArt = new Rect(MyBoxLeft, 200.0f, 120, 120);
 
         GUI.Box(tBoxRect, icon); GUI.Button(tButtonRect, "Click"); GUI.Box(tBoxArt, icon2);
     }
 
     void Update()
     {
 
         if (Input.GetKeyDown("space")) { AnimateBox(); }
 
     }
 
     void AnimateBox()
     {
 
         if (MyBoxLeft == -200.0f)
         {
 
             while (MyBoxLeft < 20.0f)
             {
                 MyBoxLeft += 5.0f;
                 yield return 0;
             }
 
         }
         else if (MyBoxLeft == 20.0f)
         {
 
             while (MyBoxLeft > -200.0f)
             {
                 MyBoxLeft -= 5.0f;
                 yield return 0;
             }
 
         }
 
     }
 }

I know that I need to make the void AnimateBox() to a IEnumerator for it to say it works, but it will not scroll.