How i will call native Dll from C# application.

using System;
using System.Runtime.InteropServices;
class Test
{
   [DllImport("user32.dll")]
   public static extern int
      MessageBox(IntPtr h, string m,
         string c, int type);
   public static void Main()
   {
      int retval = MessageBox(IntPtr.Zero, "text", "title", 0);
   }
}