connection - .net 3.5: To read connectionstring from app.config? -

How can read information about the connection string using the Nph API from the app.cconfig file?

The platform is pure 3.5

  & lt ;? Xml version = "1.0" encoding = "UTF-8"? & Gt; & Lt; Configuration & gt; & Lt; ConnectionStrings & gt; & Lt; Add connection String = "providerName =" "name =" "/> & lt; / ConnectionStrings & gt; & lt; / configuration & gt;  

> System.configuration