Historically, casino gaming was associated solely with the rich and famous. It was, therefore, no surprise to see dress codes strictly enforced in some of the oldest established gaming floors to make the nobility feel at ease.
Gone are the days of the Suit and Tie/Cocktail Dress  dress code for a casino. Today, just about anything goes, at least at most casinos. However, there are some casinos where you will, undoubtedly, feel more correct  if you climb up the formal dress code ladder a bit vs wearing a Tshirt and flip flops.