In web.config

<appSettings>
<add key="StudConn" value="server=SLIM\SQLEXPRESS;database=Student;uid=chian;pwd=mayyee88;"/>
</appSettings>

In .aspx

string connectionInfo = ConfigurationSettings.AppSettings["StudConn"];
SqlConnection conn = new SqlConnection(conninfo);

ENCAPSULATION

private string connection;

public static string connection
{
get
{
return ConfigurationSettings.AppSettings["StudConn"];
}
}

public SqlConnection GetConn()
{
SqlConnection conn=new SqlConnection(connection);
return conn
}

In .aspx

public void Page_Load()
{
Sqlconnection C= GetConn();
}