Sites like bittleships and luckycoin casino make it look so easy to deposit/spend/earn/withdrawl bitcoin, and I was wondering if someone would help me set that up.
It's pretty easy to do if you run your own bitcoind. You use the bitcoind JSON RPC to detect player deposits, and all other transactions are just INSERTs into your database. Then, a SQL query like this can give you the player's balance:
SELECT SUM(AMOUNT) FROM TXNS WHERE UID=[user's id];
Combine this with client-side polling, and voila!
SUM(AMOUNT) will quickly slow down your site if you plan to have millions of users. A simpler strategy is to do a small incremental computation with each transaction and record the new total balance with each transaction. That way you just need a simple SELECT to get the balance.