using System.Diagnostics;
using System.Runtime.InteropServices;

static class Program
{
    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool IsWindowVisible(IntPtr hWnd);

    public static bool IsProcessDead(Process pr)
    {
            IntPtr hwnd = pr.MainWindowHandle;
            if (hwnd == IntPtr.Zero) return true;

            return !IsWindowVisible(hwnd);
    }



    void ClearProcesses()
    {
            Process[] prs=Process.GetProcessesByName("excel");
            foreach (Process proc in prs)
            {
                if(IsProcessDead(proc))proc.Kill();
            }
     }

}