imports three functions to display the vertical and horizontal size of the screen. : Windows API : Windows C# Source Code

    
 

using System;
using System.Runtime.InteropServices;

public class Starter {
    public static void Main() {
        IntPtr hDC = API.GetDC(IntPtr.Zero);
        int v = API.GetDeviceCaps(hDC, API.HORZRES);
        Console.WriteLine("Vertical size of window {0}mm.", v);
        int h = API.GetDeviceCaps(hDC, API.HORZRES);
        Console.WriteLine("Horizontal size of window {0}mm.", h);
        int resp = API.ReleaseDC(IntPtr.Zero, hDC);
        if (resp != 1) {
            Console.WriteLine("Error releasing hdc");
        }
    }
}

public static class API {
    [DllImport("user32.dll")]
    public static extern IntPtr GetDC(IntPtr hWnd);

    [DllImport("user32.dll")]
    public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

    [DllImport("gdi32.dll")]
    public static extern int GetDeviceCaps(IntPtr hDC, int nIndex);

    public const int HORZSIZE = 4;  // horizontal size in pixels
    public const int VERTSIZE = 6;  // vertical size in pixels
    public const int HORZRES = 8;   // horizontal size in millimeters
    public const int VERTRES = 10;  // vertical size in millimeters
}