Tile function for an RPG question

programming flash
1

When I run this code it just adds one tile at 0,0. Any ideas?

        public function tile(obj:Object,times:int = 5,X:Number = 0, Y:Number = 0,Z:Number = 0, TileSize:Number = 50) {
            var a:int = 0;
            var b:int = 0;
            while(a < times) {
                addChild(new obj);
                obj.x=X+(TileSize*a);
                obj.y=Y+(TileSize*b);
                obj.z=Z;
                tileIndex.push(obj);
                if (a==(times-1)) {
                    b++;
                    if (b < times) {
                        a=-1;
                    }
                }
                a++;
            }
        }