cshttp Beginner Tutorial - Day 5: Dynamic Data & Memory State (Interactive Guestbook)
Day 5: Dynamic Data & Memory State (Interactive Guestbook)
In Day 4, when someone submitted a contact message, we received it and printed it to the console, but the message was gone once the page finished loading.
In Day 5, we build our first Stateful Web Application! We create an Interactive Guestbook where visitors can post comments, and the comments are stored in server memory (List<string>). Every visitor to your website can see all posted comments!
What You Will Learn Today
- Server-Side Memory State (
List<string>): Storing data in a static C# collection on the server. StringBuilder&foreachloop: Dynamically generating HTML list items (<li>) from our stored data.- PRG Pattern (Post-Redirect-Get): Using
Response.Redirect("/guestbook")after saving a comment so the browser refreshes cleanly without duplicate form submissions.
The Code
Update Program.cs with the following code:
using System;
using System.Collections.Generic;
using System.Text;
using cshttp;
static class Program
{
// NEW IN DAY 5: A list stored in server memory!
// Every visitor to the website shares this exact same list.
static List<string> guestbookEntries = new List<string>()
{
"[2026-10-22 09:00] System: Welcome to our new Guestbook!",
"[2026-10-22 09:05] Alice: First comment! C# web dev is awesome."
};
static void Main()
{
WebApp.Run(8080, OnRequest);
}
static void OnRequest()
{
string path = Request.Path.ToLower();
switch (path)
{
case "/":
case "/home":
HandleHome();
return;
case "/guestbook":
HandleGuestbook();
return;
case "/greet":
HandleGreet();
return;
case "/about":
HandleAbout();
return;
case "/contact":
HandleContact();
return;
default:
HandleNotFound();
return;
}
}
static void RenderPage(string title, string bodyContent)
{
string html = $@"
<html>
<head>
<title>{title}</title>
</head>
<body>
<nav>
<a href=""/"">Home</a> |
<a href=""/guestbook"">Guestbook</a> |
<a href=""/greet"">Greet</a> |
<a href=""/about"">About</a> |
<a href=""/contact"">Contact</a>
</nav>
<hr />
{bodyContent}
<hr />
<footer>
<small>Server Time: {DateTime.Now:yyyy-MM-dd HH:mm:ss}</small>
</footer>
</body>
</html>";
Response.Write(html);
Response.End();
}
// NEW IN DAY 5: Combining POST forms, C# Lists, and foreach loops!
static void HandleGuestbook()
{
// 1. If user submitted a new comment:
if (Request.Method == "POST")
{
string author = Request.Form["author"];
string comment = Request.Form["comment"];
if (!string.IsNullOrWhiteSpace(author) && !string.IsNullOrWhiteSpace(comment))
{
string timestamp = DateTime.Now.ToString("yyyy-MM-dd HH:mm");
string entry = $"[{timestamp}] {author}: {comment}";
// Add to our server list
guestbookEntries.Add(entry);
}
// Redirect back to the guestbook page so the browser refreshes cleanly
Response.Redirect("/guestbook");
return;
}
// 2. Build the HTML list of all current comments using a loop
StringBuilder listHtml = new StringBuilder();
listHtml.Append("<ul>");
foreach (string entry in guestbookEntries)
{
listHtml.Append($"<li style=\"margin-bottom: 8px;\">{entry}</li>");
}
listHtml.Append("</ul>");
// 3. Render the Guestbook form + the list of comments
string content = $@"
<h1>Community Guestbook</h1>
<p>Leave a message for everyone visiting this site!</p>
<form action=""/guestbook"" method=""post"" style=""background: #f9f9f9; padding: 15px; border: 1px solid #ddd; max-width: 450px;"">
<div>
<label>Your Name:</label><br />
<input type=""text"" name=""author"" required style=""width: 100%;"" />
</div>
<br />
<div>
<label>Your Comment:</label><br />
<textarea name=""comment"" rows=""3"" required style=""width: 100%;""></textarea>
</div>
<br />
<button type=""submit"">Sign Guestbook</button>
</form>
<hr />
<h2>Recent Entries ({guestbookEntries.Count})</h2>
{listHtml.ToString()}";
RenderPage("Guestbook", content);
}
static void HandleContact()
{
if (Request.Method == "POST")
{
string senderName = Request.Form["sender"];
string email = Request.Form["email"];
string message = Request.Form["message"];
Console.WriteLine($"[New Message] From: {senderName} ({email}) - {message}");
string thankYouContent = $@"
<h1>Thank You, {senderName}!</h1>
<p>We received your message and will reply to <b>{email}</b> soon.</p>
<div style=""background: #f0f0f0; padding: 10px; border-radius: 4px;"">
<i>""{message}""</i>
</div>
<p><a href=""/contact"">Send another message</a></p>";
RenderPage("Message Received", thankYouContent);
return;
}
string formContent = @"
<h1>Contact Us</h1>
<p>Send us a message below:</p>
<form action=""/contact"" method=""post"">
<div>
<label>Your Name:</label><br />
<input type=""text"" name=""sender"" required style=""width: 300px;"" />
</div>
<br />
<div>
<label>Email Address:</label><br />
<input type=""email"" name=""email"" required style=""width: 300px;"" />
</div>
<br />
<div>
<label>Message:</label><br />
<textarea name=""message"" rows=""5"" cols=""40"" required></textarea>
</div>
<br />
<button type=""submit"">Send Message</button>
</form>";
RenderPage("Contact", formContent);
}
static void HandleGreet()
{
string name = Request.Query["name"];
string greetingMessage;
if (string.IsNullOrEmpty(name))
{
greetingMessage = "<p>Please enter your name below, or try clicking a quick link!</p>";
}
else
{
greetingMessage = $"<h2>Hello, {name}! Welcome to C# Web Development!</h2>";
}
string content = $@"
<h1>Interactive Greeting</h1>
{greetingMessage}
<form action=""/greet"" method=""get"">
<label>Your Name:</label>
<input type=""text"" name=""name"" placeholder=""Type your name..."" />
<button type=""submit"">Say Hello</button>
</form>";
RenderPage("Greet", content);
}
static void HandleHome()
{
string content = @"
<h1>Welcome Home</h1>
<p>Check out our new <a href=""/guestbook"">Guestbook</a> to see shared server state in action!</p>";
RenderPage("Home", content);
}
static void HandleAbout()
{
string content = @"
<h1>About Us</h1>
<p>We build fast, zero-dependency web apps in C#.</p>";
RenderPage("About Us", content);
}
static void HandleNotFound()
{
Response.StatusCode = 404;
string content = @"
<h1>404 Not Found</h1>
<p>The page you are looking for does not exist.</p>";
RenderPage("404 Not Found", content);
}
}Test It in Your Browser
- Run the app (
dotnet run). - Visit
http://localhost:8080/guestbook. - Enter your name and a comment, then click Sign Guestbook.
- The page refreshes and your new comment appears in the list!
- Open an Incognito window or a different browser tab and visit the same linkâyou will see the exact same comments!