我照范例想做一个下雪的动画但是不能运行？请教哪里出错？
a = random (100 );

while (Number(a)<=100) {

a = Number (a)+1;

setProperty ("/snow", _x, random(500));

setProperty ("/snow", _y, random(400));

setProperty ("/snow", _xscale, random(50));

setProperty ("/snow", _yscale, random(50));

setProperty ("/snow", _rotation, random(360));

duplicateMovieClip ("/snow", "\"snow_\" add a", a);
}

a = 1

while (Number(a<=100) {


duplicateMovieClip ("/snow", "/snow" add a", a);

setProperty ("/snow"add a, _x, random(500));

setProperty ("/snow"add a, _y, random(400));

setProperty ("/snow"add a, _xscale, random(50));

setProperty ("/snow"add a, _yscale, random(50));

setProperty ("/snow" add a, _rotation, random(360));

a = Number (a)+1;

}