[DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr FindWindow(string strClassName, string strWindowName);

        [DllImport("user32.dll")]
        public static extern bool GetWindowRect(IntPtr hwnd, ref Rect rectangle);

        public struct Rect
        {
            public int Left { get; set; }
            public int Top { get; set; }
            public int Right { get; set; }
            public int Bottom { get; set; }
        }

......

       public static void RechnerWindowLocation()
        {
            Process[] processes = Process.GetProcessesByName("Calculator"); 
            Process lol = processes[0];                                                          
            IntPtr ptr = lol.MainWindowHandle;                                            
            Rect NotepadRect = new Rect();
            GetWindowRect(ptr, ref NotepadRect);
            MessageBox.Show($"Left:{NotepadRect.Left} Right:{NotepadRect.Right} Top:{NotepadRect.Top} Bottom:{NotepadRect.Bottom}");
        }

        private void button1_Click(object sender, EventArgs e)
        {
           RechnerWindowLocation();
        }

public struct Rect
{
    public int Left;
    public int Top;
    public int Right;
    public int Bottom;
}

        public static void RechnerWindowLocation()
        {
            Process[] processes = Process.GetProcessesByName("Calculator");
            Process lol = processes[0];
            IntPtr ptr = lol.MainWindowHandle;
            Rect NotepadRect = new Rect();
            GetWindowRect(ptr, ref NotepadRect);
            MessageBox.Show($"Left:{NotepadRect.Left} Right:{NotepadRect.Right} Top:{NotepadRect.Top} Bottom:{NotepadRect.Bottom}");
        }

        public static void RechnerWindowLocationZwei()
        {
            Rect rct;
            Rectangle myRect = new Rectangle();
            Process[] processes = Process.GetProcessesByName("Calculator");
            Process lol = processes[0];
            IntPtr ptr = lol.MainWindowHandle;
            Rect NotepadRect = new Rect();

            if (!GetWindowRect(ptr, ref NotepadRect));
            {
                MessageBox.Show("ERROR");
                return;
            }
            MessageBox.Show(rct.ToString());

            myRect.X = rct.Left;
            myRect.Y = rct.Top;
            myRect.Width = rct.Right - rct.Left + 1;
            myRect.Height = rct.Bottom - rct.Top + 1;
        }

public static void RechnerWindowLocation()
        {
            IntPtr hwnd = FindWindow(null, "Rechner");
            Rect NotepadRect = new Rect();
            GetWindowRect(hwnd, ref NotepadRect);
            MessageBox.Show($"Left:{NotepadRect.Left} Right:{NotepadRect.Right} Top:{NotepadRect.Top} Bottom:{NotepadRect.Bottom}");
        }

        

        private void button1_Click(object sender, EventArgs e)
        {
            RechnerWindowLocation();
        }