If visiting thailand can you wear shorts and t shirts?

i`m not sure if i can wear shorts and t shirts in or if i should wear trousers and long sleeves to visit temples and avoid offending locals

I understand your worries because, really you wear anything you like in Thailand except when visiting the temples.
You won't be allowed entry unless you observe proper dress code. T-shirt is ok but please avoid wearing shorts during your temple visits. For footwear, they generally let you leave the footwear outside of the temple. Some temples will require you to wear socks inside the temples. With all these minor restrictions, I think the experience of seeing the temples is all worth it

Wear what you like only when your going into temples real old temples do you wear long trousers,shorts OK in most Grand Palace, Leaning Buddha etc. Vest are out in most of temples. T-shirts are OK

Don't think thats a problem.
Trousers and Ts can't go wrong.

When visiting temples wear pants and long-sleeved shirts out of respect. When traveling elsewhere in the cities, or on beaches you can dress more casually.

It depends where you're visiting. If you plan to visit the temple, you should wear trouser with short or long sleeves (but not T's). Besides that, you're fine.

Wat Phra Kaew does have a dress code not because of the Wat itself but it is also a residence of the Royal Family Entry is limited to those properly attired. As outer garments, shorts, mini-skirts, culottes, tight-fitting trousers, tights, bare shoulders, and sleeveless shirts are not suitable, neither are sweat shirts, tracksuits, wind-cheaters, nor sandals without ankle or heel straps. Shirt sleeves must not be rolled up.

you can wear whatever you like but in the temples you must wear long trousers as not to offend

You need trousers and sleeved shirts for the temple visit. Elsewhere, shorts and tees will be fine.