<connectionStrings>
		<add name="sampleDBConnectionString" connectionString="Data Source=SQLEXPRESS;Initial Catalog=sampleDB;Integrated Security=True" providerName="System.Data.SqlClient"/>
</connectionStrings>

String connString = ConfigurationManager.ConnectionStrings["sampleDBConnectionString"].ConnectionString;

public static class DataBaseConnection 
    { 
       
private string connectionString = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;


        public static SqlConnection GetConnection(string connectionString ) 
        { 
            SqlConnection connection = null; 
            try 
            { 
                connection = new SqlConnection(connectionString); 
                connection.Open(); 
            } 
            catch (Exception ex) 
            { 
                
                if (connection != null) 
                { 
                    connection.Dispose(); 
                } 
            } 
            return connection; 
        } 
 
        
        public static SqlCommand GetCommand(this SqlConnection connection, string commandText, CommandType commandType) 
        { 
            SqlCommand command = connection.CreateCommand(); 
            command.CommandTimeout = connection.ConnectionTimeout; 
            command.CommandType = commandType; 
            command.CommandText = commandText; 
            return command; 
        } 
 
       
        public static void AddParameter(this SqlCommand command, string parameterName, object parameterValue, SqlDbType parameterSqlType) 
        { 
            if (!parameterName.StartsWith("@")) 
            { 
                parameterName = "@" + parameterName; 
            } 
            command.Parameters.Add(parameterName, parameterSqlType); 
            command.Parameters[parameterName].Value = parameterValue; 
        } 
    } 


 

<connectionStrings>
<add name="dbconnection" connectionString="Data Source=SureshDasari;Integrated Security=true;Initial Catalog=MySampleDB"/>
</connectionStrin

   public class Global : System.Web.HttpApplication
    {
        
        void Application_Start(object sender, EventArgs e)
        {            
            // Code that runs on application startup
            Application["DBCon"] = @"Data Source=SIVA-PC\sqlexpress;Initial Catalog=ShivaDB;Integrated Security=True";
        }


        protected void Page_Load(object sender, EventArgs e)
        {   
SqlConnection sqlcon = new SqlConnection(Application["DBCon"].ToString());
 sqlcon.Open();
}

   public partial class WebForm1 : System.Web.UI.Page
    {
        public static string GlobalDBConString = @"Data Source=SIVA-PC\sqlexpress;Initial Catalog=ShivaDB;Integrated Security=True";
        
        protected void Page_Load(object sender, EventArgs e)
        {

        }


   public partial class _Default : System.Web.UI.Page
    {
        
        protected void Page_Load(object sender, EventArgs e)
        {            
            SqlConnection sqlcon = new SqlConnection(WebForm1.GlobalDBConString); 
                sqlcon.Open();

      public static SqlConnection DbConnect(SqlConnection sqlConn)
        {
            sqlConn.ConnectionString = @"Data Source=SIVA-PC\sqlexpress;Initial Catalog=ShivaDB;Integrated Security=True";
            return sqlConn;
        }


   public partial class _Default : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection();
            WebForm1.DbConnect(con);
            con.Open();