var prevId:uint;

for (var n:uint = 0; n < 10; n++) {
	var btn:MovieClip = this["btn" + n];
	btn.id = n;
	btn.addEventListener(MouseEvent.CLICK, click, false, 0, true);
}

function click(evt:MouseEvent):void {
	var currentId:uint = evt.target.id;
	var currentBtn:MovieClip = this["btn"+currentId];
	currentBtn.gotoAndPlay("on");
	var prevBtn:MoiveClip = this["btn"+prevId];
	if (prevBtn) prev_btn.gotoAndPlay("off");
	prevId = currentId;
}