Dice odds: Simulating a game of Craps

Question

My brother turns 21 in a couple of weeks and my parents and I are taking him to Las Vegas. For my 21st, I brought $200 to gamble in Vegas and came home with around $450, mostly from playing craps. I plan on bringing $200 again for this trip and before I go I thought I'd run some craps simulations to see if I can double my money again.

I've read from several sources that the house has the smallest advantage in craps when placing a passline bet with maximum odds. From my memory, and as surveyed by Wizard of Odds, most casinos on the Strip are 3-4-5 odds with a $5 minimum. Taking this into account, here is a simulation of a craps session (of 100 dice rolls) in PHP:

<?php

$stash = 200;
$bet = 5;

for($i=100; $i--;) {

    $dice1 = mt_rand(1, 6);
    $dice2 = mt_rand(1, 6);
    $total = $dice1 + $dice2;

    if(!$button) {
        if($total===7 || $total===11) {
            $stash += $bet;
        }
        elseif($total===2 || $total===3 || $total===12) {
            $stash -= $bet;
        }
        else {
            $button = $total;
            if($total===4 || $total===10) {
                $odds = $bet*3;
            }
            elseif($total===5 || $total===9) {
                $odds = $bet*4;
            }
            elseif($total===6 || $total===8) {
                $odds = $bet*5;
            }
        }
    }
    else {
        if($total===7) {
            $button = 0;
            $stash -= ($bet + $odds);
        }
        elseif($total===$button) {
            $button = 0;
            $stash += $bet;
            if($total===4 || $total===10) {
                $stash += $odds*2/1;
            }
            elseif($total===5 || $total===9) {
                $stash += $odds*3/2;
            }
            elseif($total===6 || $total===8) {
                $stash += $odds*6/5;
            }
        }
    }

    echo 'Stash: $'.$stash.'<br/>';

}

?>

Is there anything wrong with my math here? While there are peaks and troughs throughout each session, this simulation more often doubles its money before going broke. Considering the house always has the edge in craps, even if it's just a fraction of a percent, I'm perplexed by this result.

Answer 1

Well, right off the bat, I can see that you've got an error in the simple 7 or 11 win case: You're supposed to win your bet, not twice your bet.

Edit: I believe the payout for the odds bet is commensurate with the actual probability. You are twice as likely to roll 7 (lose your odds) than 10, so you should get paid 2:1 when you win on a 4 or 10; and only paid 6:5 when you win on a 6 or 8.