C#: using Win32API Functions

using System.Windows.Forms;
using System.Runtime.InteropServices;
using System;
using System.Drawing;

public class Window : Form
{
	[DllImport("user32.dll")]
	public static extern int MessageBox(int h, string m, string c, int type);
	
	[DllImport("kernel32")]
	static extern void GetSystemInfo(ref SYSTEM_INFO pSI); 
	
	[DllImport("user32.dll")]
	static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
								
	
	[StructLayout(LayoutKind.Sequential)]
	public struct SYSTEM_INFO {
		public uint dwOemId;
		public uint dwPageSize;
		public uint lpMinimumApplicationAddress;
		public uint lpMaximumApplicationAddress;
		public uint dwActiveProcessorMask;
		public uint dwNumberOfProcessors;
		public uint dwProcessorType;
		public uint dwAllocationGranularity;
		public uint dwProcessorLevel;
		public uint dwProcessorRevision;
	}
	
	
	public Window()
	{
		Button bt = new Button();
		bt.Location = new Point(20,30);
		bt.Click += bt_Click;
		Controls.Add(bt);
	}
	
	void bt_Click(object sender, EventArgs e)
	{
		//MessageBox(0, "API message box", "API demo", 0);
		try
		{
			SYSTEM_INFO s = new SYSTEM_INFO();
			GetSystemInfo(ref s);
			
			MessageBox(0, s.dwNumberOfProcessors.ToString(), "API demo", 0);
		}
		catch(Exception) {}
	}
	
	static void Main()
	{
		Application.Run(new Window());
	}
}