private void Submit(object sender, EventArgs e)
{
if (comboBox1.SelectedIndex.Equals(0) || comboBox2.SelectedIndex.Equals(0) || comboBox3.SelectedIndex.Equals(0))
{
SystemManager.ShowMessageBox("Date, Month, and Year required, please fill them!", "Information", 1);
}
else
{
int visitorAge = comboBox3.SelectedIndex - DateTime.Now.Year;
SystemManager.AddAge(visitorAge, Convert.ToString(DateTime.Now));
}
}