Introduction and examples of hidden fields in HTML

<form action="value increment.ashx" method="post">
<input type="hidden" name="_viewstate" value="a" />
<input type="hidden" name="_div" value="@n" />
<!-- <input name="txt" type="text" value="@value" />-->
<div>@n</div>
<input type="submit" value="click" />
</form>

int n = 0;
public void ProcessRequest (HttpContext context) {
context.Response.ContentType = "text/html";

string path = context.Request.MapPath("value increment.htm");
string html = System.IO.File.ReadAllText(path);
// Check if the page is loaded for the first time
string viewstate = context.Request.Form["_viewstate"];
if (!string.IsNullOrEmpty(viewstate))
{
//Click the post button
//Get the value of the hidden field
string s = context.Request.Form["_div"];
if (int.TryParse(s, out n))
{
n++;
html = html.Replace("@n",n.ToString());
}
}
else
{
//The page is loaded for the first time, assign values ​​to div and the hidden fields corresponding to div
html = html.Replace("@n", n.ToString());
}
context.Response.Write(html);
}