登陆界面。。新人求指教，谢谢

一点都不懂

我做的是排课系统，下面是我登陆界面的全部代码，可是调试显示下面红色处的else后面要添加；且else属于无效的表达式，应该怎么改正呢？求指教，谢谢！
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace WindowsFormsApplication1
{
    public partial class denglu : Form
    {
        public static string quanxian;
        public denglu()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn =   PK.DB.DBconn.stucon();
            conn.Open();
            SqlCommand cmd = null;
if (radioButton1.Checked)
{
string sql = "select count(*) from admin where  name='" + textBox1.Text + "' and  pwd='" + textBox2.Text + "' and quanxian='管理员'";
cmd = new SqlCommand(sql, conn);
quanxian = "管理员";
            }            
else if(radioButton2.Checked)
{
string sql = "select count(*) from admin where  name='" + textBox1.Text + "' and pwd='" + textBox2.Text + "' and quanxian='教师'";
cmd = new SqlCommand(sql, conn);
quanxian= "教师";
            }
else if(radioButton3.Checked)
{
string sql = "select count(*) from admin where  name='" + textBox1.Text + "' and pwd='" + textBox2.Text + "' and quanxian='学生'";
cmd = new SqlCommand(sql, conn);
quanxian= "学生";
            }
{
    Form1 frm = new Form1();
    frm.Show();
    this.Hide();
  }
            else
                MessageBox.Show("用户名和密码错误");
        }
private void button2_Click(object sender, EventArgs e)
{
            Environment.Exit(0);
        }
private void radioButton1_CheckedChanged(object sender, EventArgs e)
        {
            }
        private void button2_Click_1(object sender, EventArgs e)
        {
            Application.Exit();
        }
        }
    }

songwenqi

[C#] 纯文本查看 复制代码

else if(radioButton3.Checked) 
{
string sql = "select count(*) from admin where  name='" + textBox1.Text + "' and pwd='" + textBox2.Text + "' and quanxian='学生'";
cmd = new SqlCommand(sql, conn);
quanxian= "学生";
            }
//=======这里有问题
{
    Form1 frm = new Form1();
    frm.Show();
    this.Hide();
  }
//================
            else
                MessageBox.Show("用户名和密码错误");
        }

一点都不懂

谢谢，我改过来了，我在那里添加了
int i = Convert.ToInt32(cmd.ExecuteScalar());
if (i > 0)