Output string to GUI using int switch case

Hi, I'm currently trying to convert int values to string values that can be used in Unity's GUI canvas. However, my code still only shows the int value on the GUI when "plane" value is changed.

 public static int plane;
 const string isTop = "Top";
 const string isCenter = "Center";
 const string isBottom = "Bottom";

 public virtual string WhatPlane()
 {
     switch (plane)
     {
         case 0:
             return isTop;
         case 1:
             return isCenter;
         case 2:
             return isBottom;
         default:
             break;
     }
     return null;
 }