<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>下拉菜单DEMO</title>
<link rel="stylesheet" type="text/css" href="/cdn.bootcss.com/bootstrap/3.3.2/css/bootstrap.min.css" />
</head>
<body><!-- 下拉菜单 --><div class="btn-group dropdown"><button class="btn btn-default dropdown-toggle" data-toggle="dropdown"> 选择... <span class="caret"></span></button><ul class="dropdown-menu"><li><a href="#">Item 1</a></li><li><a href="#">Item 2</a></li><li><a href="#">Item 3</a></li><li><a href="#">Item 4</a></li></ul></div>
<br/>
<br/>
<br/>
<br/>
<br/>
<br/>
<br/><!-- 上拉菜单 --><div class="btn-group dropup"><button class="btn btn-default dropdown-toggle" data-toggle="dropdown"> 选择... <span class="caret"></span></button><ul class="dropdown-menu"><li><a href="#">Item 1</a></li><li><a href="#">Item 2</a></li><li><a href="#">Item 3</a></li><li><a href="#">Item 4</a></li></ul></div>
<br/>
<br/>
<br/>
<br/>
<!-- <div> -->
<!-- <div class="col-md-3"> -->
<!-- <select class="form-control"> -->
<!-- <option value="1">Item 1</option> -->
<!-- <option value="2">Item 2</option> -->
<!-- <option value="3">Item 3</option> -->
<!-- <option value="4">Item 4</option> -->
<!-- </select> -->
<!-- </div> -->
<!-- </div> --><!-- 基础的Jquery -->
<script type="text/javascript" src="/cdn.bootcss.com/jquery/3.3.1/jquery.min.js" ></script>
<!-- 基础的bootstrap -->
<script type="text/javascript" src="/cdn.bootcss.com/bootstrap/3.3.2/js/bootstrap.min.js" ></script>
<script type="text/javascript">$(function(){});
</script>
</body>
</html>效果：
bootstrap和jQuery下载地址：
https://download.csdn.net/download/Bof_jangle/88614214
的各种操作（入栈，出栈，判断栈非空，判断栈已满，附源码）)
