c# controle another application, press buttons

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {

        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(String sClassName, String sAppName);

        [DllImport("user32.dll")]
        public static extern int SendMessage(int hWnd, uint Msg, int wParam, int lParam);

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

            // Find and save calculator as thisWindow
            IntPtr thisWindow = FindWindow(null, "Calculator");


            //Press button "8" on calulator app
            SendMessage((int)thisWindow, 006303C8, 0, IntPtr.Zero);




        }
    }
}&lt;/pre&gt;</pre>