Thanks for the reply. BTW, I've rolled a card. I couldn't get the result if I won or not. How can I get the result of the roll?
Once you triggers the ROLL game, its result will be came out about 1~2 minutes later. it depends on the status of ethereum network.
When ROLL is triggered, our smart contract gets a fresh random number seed from the Wolfram Alpha, via Oraclize library.
from this number, we just take last two-digit : range from [0,99]
if this random number is smaller than 50, user wins. otherwise, user loses. it's very simple and provable.
This is link to the contract code (Decoding roll result) :
https://github.com/ether-arts/ether-arts/blob/e2b9f27137768b2722ec247c9968f9463f17e4bf/contracts/EAO_roll.sol#L99if you are familar with code, checking this part will be helpful.