What is Top-Level Program in C# 9 and Later?

Starting with C# 9, Microsoft introduced top-level programs — a new syntax feature that simplifies writing simple applications by eliminating the need for boilerplate code like Main methods and class declarations.

This article explains what top-level programs are, why they were introduced, and how you can use them to write cleaner, faster-to-read code.

What Is a Top-Level Program?

In C# versions prior to 9, every program required at least the following structure:

using System;

namespace MyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }
}

Starting with C# 9, you can skip all that boilerplate and write:

using System;

Console.WriteLine("Hello, World!");

This is called a top-level program — the compiler automatically wraps your code in a class and generates the Main method for you.

Why Was It Introduced?

Top-level programs were added to make C# simpler for:

• Beginners who want to write short programs without extra ceremony
• Scripts and small utilities where you don’t need a full project structure
• Tutorials and documentation where concise examples are clearer

It reduces visual noise and makes small programs more approachable.

How Does It Work?

When you write a top-level program:

✅ Only one file in the project can have top-level statements.
✅ The compiler generates an implicit Main method that wraps your code.
✅ You can still access command-line arguments using the args variable.

Example with arguments:

Console.WriteLine($"Number of args: {args.Length}");
foreach (var arg in args)
{
    Console.WriteLine(arg);
}

Best Practices

• Use top-level programs for small console apps, samples, or quick tests.
• For larger or production apps, stick to the classic explicit Main structure for clarity and flexibility.
• You can combine top-level statements with functions or methods declared in the same file.

Example: Mixing Functions

SayHello();

void SayHello()
{
    Console.WriteLine("Hello from a local function!");
}

Advanced Usage

You can also work with:

• async code: mark the top-level context as async.
• Dependency injection: wire up services as usual if using minimal APIs in ASP.NET Core.

Example with async:

using System.Net.Http;

using var client = new HttpClient();
var content = await client.GetStringAsync("https://example.com");
Console.WriteLine(content);

Summary

Top-level programs in C# 9+ are a powerful simplification, especially for quick scripts, demos, and educational materials. By removing unnecessary scaffolding, they let you focus on the core logic.

In tomorrow’s article, we’ll dive into async and await in C# — how to write efficient asynchronous code that doesn’t block your application.

Stay tuned!