AudioClip array not working

I have a problem with AudioClip arrays;

Here is my code:

 public AudioClip[] shootSound;
 
 void Update () {
     
     if(Input.GetMouseButtonDown(0)) {
 
         audio.clip = shootSound[0];
         audio.Play();
     }
 }

Every time I press the button I get this message:

 IndexOutOfRangeException: Array index is out of range.
 Player.Update () (at Assets/Script/Player/Player.cs:60)

But the sound is playing!

The strage thing is when i trying to get the lenght of the array the debugger is telling me that it doensnt have such a variable but monoDevelop is telling me everything is fine.

 Assets/Script/Player/Player.cs(62,46): error CS1061: Type `UnityEngine.AudioClip[]' does not contain a definition for `length' and no extension method `length' of type `UnityEngine.AudioClip[]' could be found (are you missing a using directive or an assembly reference?)

Thanks RaverTiny