private void signinbtn(object sender, EventArgs e)
        {
            Sign_in signin = new Sign_in();

            signin.Show();
            this.Close();
        }
        public void validate_signup(string username, string password, string repassword, string profilenme)
        {
            bool        valid = true; string notvalid = "";
            sql_queries query = new sql_queries("Data Source=(local);Initial Catalog=Auction_mangement_system;Integrated Security=True");

            for (int i = 0; i < username.Length; i++)
            {
                if (!char.IsDigit(username[i]) && !char.IsLetter(username[i]))
                {
                    notvalid = "username";
                    valid    = false;
                }
            }
            for (int i = 0; i < password.Length; i++)
            {
                if (!char.IsDigit(password[i]) && !char.IsLetter(password[i]))
                {
                    notvalid = "password";
                    valid    = false;
                }
            }
            for (int i = 0; i < profilenme.Length; i++)
            {
                if (!char.IsDigit(profilenme[i]) && !char.IsLetter(profilenme[i]))
                {
                    notvalid = "profile_name";
                    valid    = false;
                }
            }

            if (!valid)
            {
                MessageBox.Show("The " + notvalid + " must contain only letters and digits !");
            }
            else if (username == "" || password == "" || profilenme == "")
            {
                MessageBox.Show("Fill the username , password and profile name first");
            }
            else if (password.Length > 10 || password.Length < 5)
            {
                MessageBox.Show("The password should be between 5 and 10 characters ");
            }
            else if (username.Length > 10 || username.Length < 5)
            {
                MessageBox.Show("The username should be between 5 and 10 characters ");
            }
            else if (profilenme.Length > 10 || profilenme.Length < 5)
            {
                MessageBox.Show("The profile name should be between 5 and 10 characters ");
            }
            else if (repassword.Length == 0)
            {
                MessageBox.Show("Confirm the password");
            }
            else if (repassword != password)
            {
                MessageBox.Show("The two password don't match !");
            }
            else
            {
                if (query.check_username(username))
                {
                    MessageBox.Show("This username is already taken!");
                }
                else
                {
                    query.insert_user_information(profilenme, username, password);
                    MessageBox.Show("Registrated successifly!");
                    Sign_in    signin     = new Sign_in();
                    MainWindow mainWindow = new MainWindow();
                    mainWindow.Close();
                    signin.Show();
                }
            }
        }