Database connection

Method1
{
cn.Open();
string ster="select *from Employee";
cmd.CommandText=Str;
cmd.Connection=cn;
dr=cmd.ExecuteReader()
if(!dr.Read())
{
string TempVar=(string) dr.GetValule(0);
drpEmployee.Items.Add(TempVar);
}
}
Method2
To fill DataGrid
{
cn.Open();
ds.Clear(0
string str="select *from Employee";
cmd.CommandTex=str;
cmd.Connection=cn;
da.SelectCommand=cmd;
da.Fill(ds,"Test");
gridEmployee.DataSource=ds;
gridEmployee.DataMember="Test";
gridEmployee.DataBind();
}
Method3
using System.Data.SqlClient;
Using System.Configuration;

Public Sql Connection cn=new SqlConnection(ConfigurationSetting.AppSettings.Get("ConnectionString")
public SqlCommand cmd=new SqlCommand();
public SqlDataAdaptor da=new SqlDataAdaptor();
Button Click
{
cn.Open();
cmd=new SqlCommand("School_Add",cn);
cmd.CommandType=CommandType.StoredProcedure;
SqlParameter parStudentName=new SqlParameter("@StudentName",SqlDbType.Varchar,50);
parStudentName.Value=this.txtStudentName.Text;
cmd.Parameters.Add(parStudentName);
"
"
cmd.ExecuteNonQuery();

}