Question

Why set it to null first ?

[EDIT]

there was this code about reading some file..it was like

StreamReader sr=null;
StreamReader sr= new StreamReader("file.txt");

I asked why would you set “SR” as null first BEFORE referencing the file u wanna read

Answer 1

There is no need to do that…
in fact, the code above should give you a compile error as sr is already defined.

And you should probably write it as

using (var sr = new StreamReader("file.txt"))
{
        //code here
}

in order to make sure it is properly disposed after usage (lookup IDisposable)