Get ConnectionString from app.config

Question

I'm pretty sure there's some quick and easy error in this code but somehow I've spent the last 2 hours with this and couldn't solve it.

App.config:

<configuration>
  <connectionStrings>
    <add name="BO"
        connectionString="Data Source=MyServer;Initial Catalog=BO;User ID=WebUser;Password=MyPasswd"
        providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

Class.cs:

string connectionString = getNewConnection();
using (SqlConnection conn = new SqlConnection(connectionString)) { code }

Method.

public static string getNewConnection()
{
   return ConfigurationManager.ConnectionStrings["BO"].ConnectionString;
 }

Error:

Object reference not set to an instance of an object

on the line :

return ConfigurationManager.ConnectionStrings["BO"].ConnectionString;

EDIT:

Answer 1

It should be:

ConfigurationManager.ConnectionStrings["BO"].ConnectionString;

Edit:

You will need the corresponding libraries as well if you don't have them yet, as mentioned in the below answers I think its System.Configuration

So in full you should have:

public static string getNewConnection()
{
    return ConfigurationManager.ConnectionStrings["BO"].ConnectionString;
}

Answer 2

Use these codes in the Class :

class Connection
    {
        public static string con
        {
            get
            {
                return System.Configuration.ConfigurationManager.ConnectionStrings["sql"].ConnectionString;
            }
        }
    }