Accessing database connection string using app.config in C# winform

I can’t seem to be able to access the app.config database connection string in my c# winforms app.

app.config code

   <connectionStrings>
      <add name="MyDBConnectionString" providerName="System.Data.SqlClient"
            connectionString="Data Source=localhost;Initial Catalog=MySQLServerDB; Integrated Security=true" />
   </connectionStrings>  

C# code:

SqlConnection conn = new SqlConnection();
conn.ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["MyDBConnectionString"];    

When I try the C# code, I get a message:
Warning 1 ‘System.Configuration.ConfigurationSettings.AppSettings’ is obsolete: ‘ This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.AppSettings’

However, when I try to use:

conn.ConnectionString = System.Configuration!System.Configuration.ConfigurationManager.AppSettings["MyDBConnectionString"];  

I get an error: Only assignment, call, increment, decrement, and new object expressions can be used as a statement

Answer

This is all you need:

System.Configuration.ConfigurationManager.ConnectionStrings["MyDBConnectionString"].ConnectionString;