ASP.NET SQL CONNECTIVITY USING WEB.CONFIG

Enter the following connection string in the web config as shown below 

<connectionStrings>

      <add name="SQLCON" connectionString="Data Source=OFFICE-PC\SQLEXPRESS;Initial            Catalog=databasename;Integrated Security=true;User id=sa;Password=;"/>

</connectionStrings>

Call the above in the aspx.cs page as shown below in the page load or as public

//Use this sql namespace at the starting along with the other namespaces as shown 
Using System.Data.SqlClient

//Calling the Connectionstring

static string strcon = ConfigurationManager.ConnectionStrings["SQLCON"].ConnectionString;
//Create new sqlconnection and connection to database by using connection string from web.config file SqlConnection con = new SqlConnection(strcon);