can I paint decking floor with ordinary paint?.what is hardest wearing? decking paint used previously

If you don't want to strip and sand it, then an exterior house paint is your only option. But, you can then paint over the paint with a clear Polyurethane to get maybe a few years at a time out of the polyurethane. But, you'll need to strip everything in 10-years.

- Otherwise, it should've never been painted and only Solid Stained. Stain doesn't peel, blister or crack and just fades. If it gets Sun and you're fine with the wood-look, then One-Time Wood Protector