cmbSelect.SelectedIndex

（cmbSelect）为自定义的下拉框name；cmbSelect.SelectedIndex表示下拉框内集合的序号，由0开始计起。

例如：

 1 int i = cmbSelect.SelectedIndex;
 2                 switch (i)
 3                 {
 4                     case 0:
 5                         sql1 = "select * from Student where sno='" + texSelect.Text.Trim() + "'";
 6                         break;
 7                     case 1:
 8                         sql1 = "select * from Student where sname like   '%" + texSelect.Text.Trim() + "'";
 9                         break;
10                     case 2:
11                         sql1 = "select * from Student where sex like   '%" + texSelect.Text.Trim() + "'";
12                         break;

自己真的是好菜啊，呃啊啊啊啊。。。