using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;

namespace jsglxt
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        OleDbConnection conn = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;data source=dl.mdb");

        private void button2_Click(object sender, EventArgs e)
        {
            Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string strName = textBox1.Text;
            string strPwd = textBox2.Text;
            string strRole = comboBox1.Text;
            string strOleDb = null;
            
            if (strRole == "学生")
            {
                strOleDb = "SELECT * From 登录 WHERE flag=2 AND Username='" + strName + "' AND password='" + strPwd + "'";
            }
            else if (strRole == "教师")
            {
                strOleDb = "SELECT * From 登录 WHERE flag=1 AND Username='" + strName + "' AND password='" + strPwd + "'";
            }
            else if (strRole == "管理员")
            {
                strOleDb = "SELECT * From 登录 WHERE flag=0 AND Username='" + strName + "' AND password='" + strPwd + "'";
            }
            else
            {
                MessageBox.Show("请选择用户类型");
                return;
            }

            OleDbCommand cmd = new OleDbCommand(strOleDb, conn);
            conn.Open();
            OleDbDataReader reader = cmd.ExecuteReader();

            if (reader.Read())
            {
                if (comboBox1.Text == "学生")
                {
                    Form2 studentform = new Form2();
                    //studentform.setStateName(strName);
                    studentform.Show();
                    ;
                    this.Visible = false;
                }
                if (comboBox1.Text == "教师")
                {
                    Form2 teacherform = new Form2();
                    //adminform.setStateName(strName);
                    teacherform.Show();
                    ;
                    this.Visible = false;

                }
                if (comboBox1.Text == "管理员")
                {
                    Form3 adminform = new Form3();
                    //adminform.setStateName(strName);
                    adminform.Show();

                    this.Visible = false;
                }
            }
            else
            {
                MessageBox.Show("用户名或密码错误！");
            }
        }

    }
}
编译说数据类型不对  不知道为什么  我用的Access数据库（.mdb） OleDbCommand cmd = new OleDbCommand(strOleDb, conn);编译时这句话出现上述错误   数据类型没有错啊

OleDbCommand cmd = new OleDbCommand(strOleDb, conn);你这句话得到的什么数据连接对象？OleDbCommand cmd = new OleDbCommand(strOleDb, conn);你这句话得到的什么数据连接对象？

看这个写法应该是oracle的链接

我vs2010编译上述代码无异常