[生成指定位数的随机数](%E7%94%9F%E6%88%90%E6%8C%87%E5%AE%9A%E4%BD%8D%E6%95%B0%E7%9A%84%E9%9A%8F%E6%9C%BA%E6%95%B0.md) [生成图形验证码](%E7%94%9F%E6%88%90%E5%9B%BE%E5%BD%A2%E9%AA%8C%E8%AF%81%E7%A0%81.md)