.net答案

private void button1_Click(object sender, EventArgs e)
{     oleDbConnection1.Open();
       if (oleDbConnection1.State == ConnectionState.Open)
           label1.Text = "成功连接到Access数据库";
       else
           label1.Text = "不能连接到Access数据库";
       oleDbConnection1.Close();
}


string mystr,mysql;
OleDbConnection myconn = new OleDbConnection();
OleDbCommand mycmd = new OleDbCommand();
mystr = "Provider = Microsoft.Jet.OLEDB.4.0;" +
          "Data Source = H:\\C#2005\\school.mdb";
myconn.ConnectionString = mystr;
myconn.Open();
mysql = "SELECT AVG(分数) FROM score";
mycmd.CommandText = mysql;
mycmd.Connection = myconn;
textBox1.Text = mycmd.ExecuteScalar().ToString();
myconn.Close();


private void button1_Click(object sender, EventArgs e)
{    string mystr,mysql;
     OleDbConnection myconn = new OleDbConnection();
     OleDbCommand mycmd = new OleDbCommand();
     mystr = "Provider = Microsoft.Jet.OLEDB.4.0;" +
          "Data Source = H:\\C#2005\\school.mdb";
    myconn.ConnectionString = mystr;
    myconn.Open();
     mysql = "SELECT AVG(分数) FROM score WHERE 学号=@no";
     mycmd.CommandText = mysql;
     mycmd.Connection = myconn;
     mycmd.Parameters.Add("@no", OleDbType.VarChar, 5).Value =
     textBox1.Text;     //设置参数值
     textBox2.Text = mycmd.ExecuteScalar().ToString();
     myconn.Close();
}


private void button1_Click(object sender, EventArgs e)
{   string mystr,mysql;
      OleDbConnection myconn = new OleDbConnection();
      OleDbCommand mycmd = new OleDbCommand();
      mystr = "Provider = Microsoft.Jet.OLEDB.4.0;" +
          "Data Source = H:\\C#2005\\school.mdb";
      myconn.ConnectionString = mystr;
      myconn.Open();
      mysql = "SELECT * FROM student";
      mycmd.CommandText = mysql;
      mycmd.Connection = myconn;
     OleDbDataReader myreader = mycmd.ExecuteReader();
      listBox1.Items.Add("学号\t姓名\t性别\t民族\t班号");
      listBox1.Items.Add("=================================");
      //循环读取信息
      while (myreader.Read())
              listBox1.Items.Add(String.Format("{0}\t{1}\t{2}\t{3}\t{4}",
                              myreader[0].ToString(), myreader[1].ToString(),
                       myreader[2].ToString(), myreader[3].ToString(),
                       myreader[4].ToString()));
       myconn.Close();
       myreader.Close();
}


namespace Proj13_1
{   public partial class Form9 : Form
      {     BindingSource mybs = new BindingSource();   //类变量
            public Form9()
            {
                    InitializeComponent();
            }
private void Form9_Load(object sender, EventArgs e)
     {    string mystr,mysql;
          OleDbConnection myconn = new OleDbConnection();
          DataSet myds = new DataSet();
          mystr = "Provider = Microsoft.Jet.OLEDB.4.0;" +
                     "Data Source = H:\\C#2005\\school.mdb";
          myconn.ConnectionString = mystr;
          myconn.Open();
          mysql = "SELECT * FROM student";
          OleDbDataAdapter myda = new OleDbDataAdapter(mysql, myconn);
          myda.Fill(myds, "student");
          mybs = new BindingSource(myds, "student");
             //用数据源myds和表student创建新实例mybs
          Binding mybinding1 = new Binding("Text", mybs, "学号");
          textBox1.DataBindings.Add(mybinding1);
          Binding mybinding2 = new Binding("Text", mybs, "姓名");
          textBox2.DataBindings.Add(mybinding2);
          Binding mybinding3 = new Binding("Text", mybs, "性别");
          textBox3.DataBindings.Add(mybinding3);
          Binding mybinding4 = new Binding("Text", mybs, "民族");
          textBox4.DataBindings.Add(mybinding4);
          Binding mybinding5 = new Binding("Text", mybs, "班号");
          textBox5.DataBindings.Add(mybinding5);
          myconn.Close();
      }
      private void button1_Click(object sender, EventArgs e)


             {    if (mybs.Position != 0)
                         mybs.MoveFirst();   //移到第一个记录
             }
             private void button2_Click(object sender, EventArgs e)
             {    if (mybs.Position !=0)
                         mybs.MovePrevious();   //移到上一个记录
             }
             private void button3_Click(object sender, EventArgs e)
             {     if (mybs.Position != mybs.Count - 1)
                         mybs.MoveNext();   //移到下一个记录
             }
             private void button4_Click(object sender, EventArgs e)
             {     if (mybs.Position != mybs.Count - 1)
                        mybs.MoveLast();   //移到最后一个记录
             }
      }
}


private void Form13_Load(object sender, EventArgs e)
{     string mystr,mysql;
      OleDbConnection myconn = new OleDbConnection();
      DataSet myds = new DataSet();
      mystr = "Provider = Microsoft.Jet.OLEDB.4.0;" +
          "Data Source = H:\\C#2005\\school.mdb";
      myconn.ConnectionString = mystr;
      myconn.Open();
      mysql = "SELECT * FROM student";
      OleDbDataAdapter myda = new OleDbDataAdapter(mysql, myconn);
      myda.Fill(myds, "student");
dataGridView1.DataSource = myds.Tables["student"];
      dataGridView1.GridColor = Color.RoyalBlue;
      dataGridView1.ScrollBars = ScrollBars.Vertical;
      dataGridView1.CellBorderStyle =
          DataGridViewCellBorderStyle.Single;
      dataGridView1.Columns[0].AutoSizeMode =
          DataGridViewAutoSizeColumnMode.AllCells;
      dataGridView1.Columns[1].AutoSizeMode =
          DataGridViewAutoSizeColumnMode.AllCells;
     dataGridView1.Columns[2].AutoSizeMode =
          DataGridViewAutoSizeColumnMode.AllCells;
     dataGridView1.Columns[3].AutoSizeMode =
          DataGridViewAutoSizeColumnMode.AllCells;
     dataGridView1.Columns[4].AutoSizeMode =
          DataGridViewAutoSizeColumnMode.AllCells;
     myconn.Close();
     label1.Text = "";
}
private void dataGridView1_CellClick(object sender,  
      DataGridViewCellEventArgs e)
{     label1.Text = "";
       try
       {     if (e.RowIndex < dataGridView1.RowCount - 1)
                   label1.Text = "选择的学生学号为:" +
             dataGridView1.Rows[e.RowIndex].Cells[0].Value;
       }
       catch(Exception ex)
       {
            MessageBox.Show("需选中一个学生记录", "信息提示");
       }
}