Calculating the previous value

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C#

private void btnUpdate_Click(object sender, EventArgs e)
        {
            ep.Clear();

            try
            {
                // Get the selected row index.
                int selectedRowIndex = dgvFacultyLeaveList.CurrentRow.Index;

                // Get the Faculty_ID of the selected row.
                string facultyID = txtID.Text.Trim();

                // Validate and get other parameters.
                string leaveType = cboLeaveType.Text.Trim();
                string totalBalance = txttotalleave.Text.Trim();
                string month = cboMonth.Text;
                string noOfDays = NoOfDays.Text;
                string leaveDate = dtpLeavedate.Value.ToString("yyyy-MM-dd");
                string leaveTime = dtpLeaveTime.Value.ToString("HH:mm:ss");
                string endDate = dtpEndDate.Value.ToString("yyyy-MM-dd");
                string endTime = dtpEndTime.Value.ToString("HH:mm:ss");
                string sanctionedLeave = txtLSanctioned.Text;
                string availedLeave = txtLAvailed.Text.Trim();
                string balance = txtBalance.Text;
                string reason = txtReasons.Text;

                // Build the SQL update query.
                string updateQuery = @"UPDATE Facultyleave SET
                                Faculty_ID = @Faculty_ID,
                                LeaveType = @LeaveType,
                                TotalBalance = @TotalBalance,
                                Month = @Month,
                                Days = @Days,
                                LeaveDate = @LeaveDate,
                                LeaveTime = @LeaveTime,
                                EndDate = @EndDate,
                                EndTime = @EndTime,
                                SancationedLeave = @SancationedLeave,
                                AvailedLeave = @AvailedLeave,
                                Balance = @Balance,
                                Reason = @Reason
                                WHERE Faculty_ID = @Faculty_ID
                                AND LeaveID = (SELECT MAX(LeaveID) FROM FacultyLeave WHERE Faculty_ID = @Faculty_ID);";

                using (var conn = DatabaseAccess.ConnOpen())
                {
                    using (var cmd = new SqlCommand(updateQuery, conn))
                    {
                        // Add parameters and values.
                        cmd.Parameters.AddWithValue("@Faculty_ID", facultyID);
                        cmd.Parameters.AddWithValue("@LeaveType", leaveType);
                        cmd.Parameters.AddWithValue("@TotalBalance", totalBalance);
                        cmd.Parameters.AddWithValue("@Month", month);
                        cmd.Parameters.AddWithValue("@Days", noOfDays);
                        cmd.Parameters.AddWithValue("@LeaveDate", leaveDate);
                        cmd.Parameters.AddWithValue("@LeaveTime", leaveTime);
                        cmd.Parameters.AddWithValue("@EndDate", endDate);
                        cmd.Parameters.AddWithValue("@EndTime", endTime);
                        cmd.Parameters.AddWithValue("@SancationedLeave", sanctionedLeave);
                        cmd.Parameters.AddWithValue("@AvailedLeave", availedLeave);
                        cmd.Parameters.AddWithValue("@Balance", balance);
                        cmd.Parameters.AddWithValue("@Reason", reason);

                        int result = cmd.ExecuteNonQuery();

                        // If the update was successful, update the DataGridView and show success message.
                        if (result > 0)
                        {
                            int updatedLeaveID = Convert.ToInt32(cmd.ExecuteScalar());

                            // Update the DataGridView row.
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[0].Value = updatedLeaveID; // LeaveID
                                                                                                        // ...

                            // Calculate updated balance and availed leave
                            int originalTotalBalance = Convert.ToInt32(totalBalance);
                            int originalAvailedLeave = Convert.ToInt32(txtLAvailed.Text);
                            int updatedNoOfDays = Convert.ToInt32(noOfDays);
                            int updatedBalance = originalTotalBalance - updatedNoOfDays;
                            int updatedAvailedLeave = originalAvailedLeave + updatedNoOfDays;


                            //int updatedLeaveID = Convert.ToInt32(cmd.ExecuteScalar());

                            // Update the DataGridView row.
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[0].Value = updatedLeaveID; // LeaveID
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[1].Value = facultyID; // Faculty ID
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[2].Value = leaveType; // Leave Type
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[3].Value = updatedBalance; // Total Balance
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[4].Value = month; // Month
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[5].Value = updatedNoOfDays; // No of Days
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[6].Value = leaveDate; // Leave Date
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[7].Value = leaveTime; // Leave Time
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[8].Value = endDate; // End Date
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[9].Value = endTime; // End Time
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[10].Value = sanctionedLeave;
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[10].Value = sanctionedLeave; // Sanctioned Leave
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[11].Value = updatedAvailedLeave; // Availed Leave
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[12].Value = balance; // Balance
                            dgvFacultyLeaveList.Rows[selectedRowIndex].Cells[13].Value = reason; // Reason

                            // Refresh the DataGridView.
                            dgvFacultyLeaveList.Refresh();

                            // Clear the input fields.
                            txtID.Text = "";
                            cboLeaveType.SelectedIndex = -1;
                            txttotalleave.Text = "";
                            cboMonth.SelectedIndex = -1;
                            NoOfDays.Text = "";
                            dtpLeavedate.Value = DateTime.Now;
                            dtpLeaveTime.Value = DateTime.Now;
                            dtpEndDate.Value = DateTime.Now;
                            dtpEndTime.Value = DateTime.Now;
                            txtLSanctioned.Text = "";
                            txtLAvailed.Text = "";
                            txtBalance.Text = "";
                            txtReasons.Text = "";
                           
                            // Show a success message.
                            MessageBox.Show("Record updated successfully!");
                            EnableComponents();
                            FillGrid("");
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                // Handle the exception gracefully.
                // For example, log the exception and display a more user-friendly message to the user.
                MessageBox.Show("Error updating the record: " + ex.Message);
            } }

What I have tried:

this is the code of my update button for Leave Module i have problem that when i want to update the leave for staff member so it calculate the previous value which is in NoOfDays textbox suppose i add leave for staff member the total balance = 10 . i add 1 leave than remaining balance =9, availed =1. so than i want to update the leave so i edit it and i remove the value which is in the textbox of NoOfDay which is =1 and write 2 so it do like add 1+2 =3 and than make balance =7, availed =3. the expected outcome should be Remaining balance = 8, availed = 2. my NoOfDays.text textbox take the previous value i add a button also that make make it 0 but its also calculate the zero when i click on the remove button to make noofdays textbox 0 it again add one value like balance =9, availed =1 when i remove the value from noofdays textbox so its become zero than it make balance = 8, availed = 2.