private void btnEdit_Click(object sender, EventArgs e)
        {
            if (dgvDiary.SelectedRows.Count == 0)
            {
                MessageBox.Show("Proszę zaznacz ucznia, którego dane chcesz edytowac");
                return;
            }
            var addEditStudent = new AddEditStudent(Convert.ToInt32(dgvDiary.SelectedRows[0].Cells[0].Value));

            addEditStudent.ShowDialog();
        }
        private void btnAdd_Click(object sender, EventArgs e)
        {
            var addEditStudent = new AddEditStudent();

            addEditStudent.ShowDialog();
        }