Day 3: Accepting User Input (URL Query String & GET Forms)

So far, our website only sends information to the visitor. But modern web apps need to interact with the visitor!

In Day 3, we teach our web server how to accept input from users. We do this with Query Strings (e.g., /greet?name=Alice) and simple HTML Forms using method="get".

What You Will Learn Today

Request.Query["name"]: Reads data sent by the browser in the URL query string (after the ?).
string.IsNullOrEmpty(): Checks if the visitor provided a name or left it blank.
Interactive HTML <form>: Lets users type their name into an input box and click a button to send it to the C# server.

The Code

Update Program.cs with the following code:

using System;
using cshttp;

static class Program
{
    static void Main()
    {
        WebApp.Run(8080, OnRequest);
    }

    static void OnRequest()
    {
        string path = Request.Path.ToLower();

        switch (path)
        {
            case "/":
            case "/home":
                HandleHome();
                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=""/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 3: Accepting user input via URL Query String & HTML Form
    static void HandleGreet()
    {
        // 1. Read the "name" parameter from the URL (e.g. /greet?name=Alice)
        string name = Request.Query["name"];

        // 2. Decide what message to show using standard C# if/else
        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>";
        }

        // 3. Render both the message AND the form so they can try again
        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>

            <p>Or test query links directly: 
                <a href=""/greet?name=Alice"">Greet Alice</a> | 
                <a href=""/greet?name=Bob"">Greet Bob</a>
            </p>";

        RenderPage("Greet", content);
    }

    static void HandleHome()
    {
        string content = @"
            <h1>Welcome Home</h1>
            <p>Click on <a href=""/greet"">Greet</a> in the menu to test user input!</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 HandleContact()
    {
        string content = @"
            <h1>Contact</h1>
            <p>Email us at [email protected]</p>";

        RenderPage("Contact", 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/greet.
Type your name into the text box and click Say Hello.
Notice how the URL changes to http://localhost:8080/greet?name=YourName, and the C# server personalizes the greeting for you!