Csharp/C Sharp by API/System.Windows.Forms/MessageBoxIcon
MessageBoxIcon.Exclamation
<source lang="csharp">
using System; using System.Windows.Forms; public class MessageBoxShowExclamation { static public void Main() { MessageBox.Show ("Hello, C# World!", "Howdy", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); } } </source>