Sorry, didn't read very carefully...

I think this will do what you want... or most of it.

DECLARE @Date1 DATE = '10-Aug-2015',

@Date2 DATE = '07-Sep-2015'

,@Diff INT

SELECT @Diff = ABS(DATEDIFF(day,@Date1,@Date2));

PRINT @Diff;

the ABS() removes the sign...