Question

What is the difference between these two ?

// Get response  
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)  
{  
    // Get the response stream  
    StreamReader reader = new StreamReader(response.GetResponseStream());  

    // Console application output  
    Console.WriteLine(reader.ReadToEnd());  
}  

without using*

// Get response  
HttpWebResponse response = request.GetResponse() as HttpWebResponse; 

// Get the response stream  
StreamReader reader = new StreamReader(response.GetResponseStream());  

// Console application output  
Console.WriteLine(reader.ReadToEnd());

Answer 1

Using requires that the object applied to it implement IDisposable, and will call the Dispose method of IDisposable when the object goes out of scope of the using block (no matter how it leaves that scope… either by execution flowing through normally, or if an Exception is thrown).

The other variant is bad practice… your resources related to response will not be cleaned up.

Note that the StreamReader is not being cleaned up in either case. You should use an inner using block to accomplish that.