Program_DMForm.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DormitoryManagment    
{
    public class DMForm : Form
    {
        protected void Navigate(ref DMForm nextForm)
        {
            this.Close();
            Thread thread = new Thread(RunForm);
            thread.Start(nextForm);
        }

        private void RunForm(object obj)
        {
            Application.Run((DMForm)obj);
        }

        protected override void OnFormClosing(System.Windows.Forms.FormClosingEventArgs e)
        {
            if (e.CloseReason != CloseReason.FormOwnerClosing)
            {
                if (Program.admin != null) Program.admin.LogOut();
                if (Program.manager != null) Program.manager.LogOut();
                if (Program.student != null) Program.student.LogOut();
            }
        }
    }
}