private void btnEdit_Click(object sender, EventArgs e)
{
var selectedId = getSelectedId();
if (selectedId < 0)
{
MessageBox.Show("Please select a student record.");
return;
}
var student = studentTable.GetStudent(selectedId);
AddStudent addStudentWindow = new AddStudent(student);
addStudentWindow.MdiParent = this.MdiParent;
addStudentWindow.Show();
}