To write formatted output Response.Output.Write() function 
is used.

The difference between Response.Write() and 
Response.Output.Write() in ASP.NET.  The short answer is 
that the latter gives you String.Format-style output and 
the former doesn't.  The long answer follows.

In ASP.NET the Response object is of type HttpResponse and 
when you say Response.Write you're really saying 
(basically) HttpContext.Current.Response.Write and calling 
one of the many overloaded Write methods of HttpResponse.  

Response.Write then calls .Write() on it's internal 
TextWriter object:

public void Write(object obj){ this._writer.Write(obj);} 

HttpResponse also has a Property called Output that is of 
type, yes, TextWriter, so:

public TextWriter get_Output(){ return this._writer; } 

Which means you can to the Response whatever a TextWriter 
will let you.  Now, TextWriters support a Write() method 
ala String.Format, so you can do this:

Response.Output.Write("Scott is {0} at 
{1:d}", "cool",DateTime.Now);

But internally, of course, this this is happening:

public virtual void Write(string format, params object[] 
arg)
{ 
  this.Write(string.Format(format, arg)); 
}