I have applied for a Long Stay Visa D to France which takes a long time to process, can i apply for a Short Stay Visa C say to Italy for a visit at the same time without affecting my first application
It's hard to prove a negative, but in general nothing stops you from getting a Schengen visa while your Type D visa is being processed. Upon receiving the Type D visa your old Schengen visa will be cancelled to avoid an overlap.
Note that the consulate might not look too kindly on such a practice, as you will potentially overstay your tourist visa if the Type D visa is denied. If you were applying for a work visa, there's also the chance that you will start working before being legally allowed to do so.