Viking is a line that has made a point not to have casinos on any of its ships, regardless of type. Most expedition ships and river boats do not have casinos. Norwegian Cruise Line's Pride of America also does not have a casino. The major exception to the big ship rule is Disney Cruise Line, which does not have a casino on any of its four cruise ships. Most large cruise ships, and even some of the smaller ones will have an onboard casino. That depends on which cruise line you've chosen.
Casino Royale on Harmony of the Seas (Photo: Cruise Critic)