Add connection string using appSetting in web.config

Add this code in web.config

  <appSettings>
    <add key="ConnectionStringName" value="Data Source=localhost;Initial Catalog=DataBaseName;User ID=SQLUserID;password=SQLPassword;" providerName="System.Data.SqlClient" />
  </appSettings>

How to read connection string in c#

string ConStr= ConfigurationSettings.AppSettings("ConnectionStringName");