private void Button_sub_Click(object sender, EventArgs e)
{
TimeClass sub = new TimeClass();
sub = t1 - t2;
label_str.Text = sub.convert_to_string();
}
private void Button_plus_Click(object sender, EventArgs e)
{
TimeClass sum = new TimeClass();
sum = t1 + t2;
label_str.Text = sum.convert_to_string();
}
private void Button_addsec_Click(object sender, EventArgs e)
{
t1.add_seconds(add);
label_str.Text = t1.convert_to_string();
}