Mono Basics

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After you get Mono installed, it’s probably a good idea to run a quick Hello World program to make sure everything is set up properly. That way you’ll know that your Mono is working before you try writing or running a more complex application.

Console Hello World

To test the most basic functionality available, copy the following code into a file called hello.cs.

using System;

public class HelloWorld
{
    public static void Main(string[] args)
    {
        Console.WriteLine ("Hello Mono World");
    }
}

To compile, use csc:

    csc hello.cs

Note: csc compiler is not available on all platforms or in very old Mono versions, in such cases use mcs instead.

The compiler will create “hello.exe”, which you can run using:

    mono hello.exe

The program should run and output:

Hello Mono World

HTTPS connections

To make sure HTTPS connections work, run the following command to check whether you can connect to nuget.org:

csharp -e 'new System.Net.WebClient ().DownloadString ("https://www.nuget.org")'

The program prints the website contents if everything works or throws an exception if it doesn’t.

WinForms Hello World

The following program tests writing a System.Windows.Forms application.

using System;
using System.Windows.Forms;

public class HelloWorld : Form
{
    static public void Main ()
    {
        Application.Run (new HelloWorld ());
    }

    public HelloWorld ()
    {
        Text = "Hello Mono World";
    }
}

To compile, use csc with the -r option to tell the compiler to pull in the WinForms libraries:

    csc hello.cs -r:System.Windows.Forms.dll

The compiler will create “hello.exe”, which you can run using:

    mono hello.exe

NOTE: on macOS you’ll have to wait around a minute the very first time you run this command. You also need to use mono32 since WinForms isn’t supported on 64bit yet. As of macOS 10.15 Catalina there’s no 32bit support anymore so WinForms doesn’t work there at the moment.

ASP.NET Hello World

Create a text file with the name hello.aspx and the content:

<%@ Page Language="C#" %>
<html>
<head>
   <title>Sample Calendar</title>
</head>
<asp:calendar showtitle="true" runat="server">
</asp:calendar>

Then run the xsp4 command from that directory:

xsp4 --port 9000

Use a web browser to contact http://localhost:9000/hello.aspx

Gtk# Hello World

The following program tests writing a Gtk# application.

using Gtk;
using System;

class Hello
{
    static void Main ()
    {
        Application.Init ();

        Window window = new Window ("Hello Mono World");
        window.Show ();

        Application.Run ();
    }
}

To compile, use mcs with the -pkg option to tell the compiler to pull in the Gtk# libraries (note that Gtk# must be installed on your system for this to work):

mcs hello.cs -pkg:gtk-sharp-2.0

The compiler will create “hello.exe”, which you can run using:

mono hello.exe