Question about the "WhileLoop" tutorial

Link to the tutorial: http://unity3d.com/learn/tutorials/modules/beginner/scripting/loops (00:00 - 01:06)

Code used to demonastrate WhileLoop

 using UnityEngine;
 using System.Collections;
 
 public class WhileLoop : MonoBehaviour
 {
     int cupsInTheSink = 4;
     
     
     void Start ()
     {
         while(cupsInTheSink > 0)
         {
             Debug.Log ("I've washed a cup!");
             cupsInTheSink--;
         }
     }
 }

Console Output:

I've washed a cup!
UnityEngine.Debug:Log(Object) I've
washed a cup!
UnityEngine.Debug:Log(Object) I've
washed a cup!
UnityEngine.Debug:Log(Object) I've
washed a cup!
UnityEngine.Debug:Log(Object)

What I don't understand is that, since cupsInTheSink variable is set to 4, why doesn't the loop just keep on going?