Why do I get this error:Expressions in a statement must be only executed by their side effects?

 var prefabBullet:Transform;
 var shootForce:float;
 private var ammo:float;
 private var shoot:float;
 
 function Start () {
 
 ammo = 5;
 shoot = 1;
 }
 
 function Update () 
 {
     if (ammo == 0)
     {
     (shoot == 0);    
     }
     
     if (shoot == 1 && (Input.GetMouseButtonDown(2)))
     {
         var    instanceBullet = Instantiate(prefabBullet, transform.position, Quaternion.identity);
         instanceBullet.rigidbody.AddForce(transform.forward * shootForce);
         ammo -=1;
     }
     
     
 }
 function OnGUI () {
     GUI.Label (Rect (10, 10, 100, 20),ammo.ToString());
 } 

Its at this part if (ammo == 0) { (shoot == 0);
}