From ASP.NET Cookies Overview:
You cannot directly modify a cookie. Instead, changing a cookie
consists of creating a new cookie with new values and then sending the
cookie to the browser to overwrite the old version on the client.
You can try this:
HttpCookie cookie = Request.Cookies["SurveyCookie"];
if (cookie == null)
{
// no cookie found, create it
cookie = new HttpCookie("SurveyCookie");
cookie.Values["surveyPage"] = "1";
cookie.Values["surveyId"] = "1";
cookie.Values["surveyTitle"] = "Definietly not an NSA Survey....";
cookie.Values["lastVisit"] = DateTime.UtcNow.ToString();
}
else
{
// update the cookie values
int newSurveyPage = int.Parse(cookie.Values["surveyPage"]) + 1;
cookie.Values["surveyPage"] = newSurveyPage.ToString();
}
// update the expiration timestamp
cookie.Expires = DateTime.UtcNow.AddDays(30);
// overwrite the cookie
Response.Cookies.Add(cookie);