ConfigurationManager ConnectionStrings not available in c#

ConfigurationManager not show ConnectionStrings until you will not add reference System.Configuration dll, right click on Project -- Add Reference after click to Assemblies then Framework and find System.Configuration dll

vs2010: Project -- Add Reference after click to .NET components and find System.Configuration dll

If also add this reference but then again its not showing its a simple way to solve you add System.Configuration.ConfigurationManager.ConnectionStrings