Copy the following code into the editor

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, world!");
        }
    }
}

Compile with mcs app.cs

Launch with mono app.exe

Launch the Mono C# REPL using csharp. With the REPL you can execute code without requiring the compiling step. Try running Console.WriteLine("Hello, world!");

Interested in writing your own C# / Mono scenarios and demos? Visit www.katacoda.com/teach