DoDo (the abbreviation of DOuble DOzen) is an implementation of card game "Twenty Four" (24), popular in China and other countries with significant Chinese population, including Australia.

The objective is very simple: to compose 24 out of four numbers, each in the range 1-10, using four arithmetic operations. A player who does it more often wins the game.

As opposed to majority of other intelligent card games, game "24" does not involve any hidden information therefore there is practically no need to remember cards or apply any long-term strategy, while fast counting is the only prerequisite to succeed. That makes "24" an ideal family game which helps to development arithmetic skills for primary school children and provides entertainment for adults at the same time.

Incidentally Dodo is a name of the bird species unique to tiny island Mauritius to the East of Africa. Dodo birds peacefully lived, eating fruits and nuts falling from trees. They didn't have any predators apart from human settlers who eventually led them to extinction in the late 17th century. Fortunately, some illustrations, descriptions as well as remains of the birds have come to us.

Dodo was the nickname of prominent English mathematician and writer Charles L. Dodgson, better known by his pen name Lewis Carroll, who invented a number of brain-teasing games, like a sort of "Scrabble" and still popular "Doublets" a.k.a. "World Links" or "World Ladder"). In his most famous novel "Alice in Wonderland" ,Dodo bird represents the author himself and, just like the author, invents a game.

——————————————

This version of game "24" encourages fast thinking. The score depends not only on the number of solved puzzles but also on the time spent on solving. If a combination has no solution, a player who figured that out is rewarded as if the puzzle is solved.

DoDo24 allows playing with one or two short (40) of full (52) packs of cards. The application also provides training mode as well as an option to enter own puzzles.

Different extensions to the game rules are available. For example, you may allow One (ace) to stand for either one or eleven in order to enlarge the variety of solvable combinations, so, for instance, "1 1 2 3" gets a solution: 11×2+3-1. Other available options are common fractions, exponentiation (raising to power), "merge" operation (writing one number after another) and presence of Zero card (Joker). Even "magic number" 24 can be changed to a different value!

DoDo 24 provides a variety of customized features. In particular, a computer solution can be presented either as sequence of operations (e.g. 6×3=18; 3×2=6; 18+6=24) or as an expression (6×3+3×2). Other customized features include choice of background texture and color, replacing standard playing card images by numbers, different types of animation.

The game can be played against the computer, or over the network (local area network, direct device connection or the Internet). Voice chat is supported for a game over the Internet.

The application supports custom background music, specified as an album or a playlist. It keeps game summaries, as well as local and online score and achievement tables. iCloud can be used for keeping summaries and local score tables, or as a backup copy of the tables.

DoDo24 is designed to run with iOS 9.0 and above. It gains advantage of newer iOS features, if available.