First, press the flag to reset your money to 100. Then, press the yellow "bet" button and choose how much you want to gamble (e.g. 50, 60). Press hit if you want to increase your total. But be warned, if you're total goes over 21, you instantly lose. But if your total is 21, you instantly win! When you're happy with your own total, press stand to reveal your opponents total and see if you won or lost!
The coding is more complicated than you think.
