有两个关于Calendar的问题，高手请进！

我是这样做的，但是有点问题， 就是它似是一个死循环
while((sj1.SelectedDate.ToOADate()<=sj3.SelectedDate.ToOADate())||(sj2.SelectedDate.ToOADate()>=sj3.SelectedDate.ToOADate()))
{
string strsql="insert into f_timing(t_kssj,t_jssj,t_txsj) values('"+sj1.SelectedDate.ToOADate()+"','"+sj2.SelectedDate.ToOADate()+"','"+sj3.SelectedDate.ToOADate()+"')";
db.ExecuteSQL(strsql);
DateTime sjx=sj3.SelectedDate.AddMonths(1);
sj3.SelectedDate=sjx;
}