"While" statement issues

Hi MATLABers,

I'm coding a version of craps (as part of a research project) to account for the number of rolls before a "7 out" accounting for (a) total rolls, (b) wins (pass line bet and (c) losses. Essentially, I want the first loop to repeat until a "point" number is established (so there could be multiple rolls/7/11/2/3/12 before the next loop takes over). Then the second loop (point cycle) continues until either (a) a point is established, then you go back to the beginning loop or (b) a 7 is rolled, which ends the hand.

M = 100000;
lost = 0; win = 0; gamelength = zeros(1,M);
data = zeros(100000,6);
for k=1:M
    curr_gamelength = 1;
    sevenout = 0;
    while (x==7) || (x==11) || (x==2) || (x==3) || (x==12)
        x = sum(round(rand(1,2)*6+0.5));
       if (x==7) || (x==11)
           win = win+1;
        elseif (x==2) || (x==3) || (x==12)
            lost = lost+1;
        else
            point = x;
       end
    end
        while point
            curr_gamelength = curr_gamelength+1;
            p = sum(round(rand(1,2)*6+0.5));
           if (p==7)
               lost=lost+1; sevenout = 1;
           elseif (p==point)
               win = win+1;
           end
               %%
        end
        gamelength(k) = curr_gamelength;
end

[Steven Lord]

The subject of your post states "While" statement issues, but you have not stated the issue that you're experiencing. I suspect I know the issue you're experiencing, but could you please state the issue explicitly?

If you're receiving an error, please show us the full text of the error message (everything displayed in the Command Window in red.)

If you're receiving a warning, please show us the full text of the warning message (everything displayed in the Command Window in orange.)

If you're receiving different results than you expected, please tell us what results you're receiving and what results you expected.

If you're having some other issue, please describe it in detail.

[Star Strider]

Note that ‘x’ has to be defined before the first while statement.

I don’t see it.

[Robert Scott]

My apologies: The latest error it returns is “x==7”. As stated earlier, defining x prior to the while statement may solve that problem.

[Robert Scott]

Here's my original code. It works, but the numbers aren't exactly right. I think the problem is that the first part of the code goes to the next loop after the first roll no matter what. However, I want it to keep rolling if the total is 7,11,2,3, or 12 (with 7 and 11 registering a win and 2,3,12 registering a loss)--but if the number is not 7,11,2,3,12 (i.e., the point number) then it goes to the next loop and that loop goes until either the point number is made (a win) or a 7 (a loss), which ends the hand. What am I doing wrong? Should I have another while statement? Thank you!

M = 10000;
lost = 0; win = 0; handlength = zeros(1,M);
data = zeros(10000,6);
for k=1:M
    sevenout = 0;
    curr_handlength = 1;
    dice = randi([1,6], 1,2);
    x = dice(1) + dice(2);
        if (x==7) || (x==11)
            win = win+1; sevenout = 0;
        elseif (x==2) || (x==3) || (x==12)
            lost = lost+1; sevenout = 0;
        else
            point = x;
        end
    while ~sevenout
        current_handlength = current_handlength+1;
        dice = randi([1,6], 1,2);
        p = dice(1) + dice(2);
        if (p==7)
            lost=lost+1; sevenout = 1;
        elseif (p==point)
            win = win+1; sevenout = 0;
        end
        %% 
    end
    handlength(k) = current_handlength;
end

[Steven Lord]

If you roll 7, 11, 2, 3, or 12 initially the current game ends. You only want to run the code to handle the point case if you rolled a different number. So why not move the code that handles the point case into the else where you set the point? That way the "win or lose on first throw" cases never see it.

By the way, craps is a straightforward enough game with pretty basic rules, but I encourage you to develop the habit of commenting your code. In this case, starting with a skeleton of comments outlining the "workflow" of a game of craps (before even writing a line of code) might be useful in planning out and keeping track of exactly what steps to execute when.

% First throw
% If first throw is a 7 or 11, win
% If first throw is a 2, 3, or 12, lose
% Otherwise the point is equal to the first throw
%   Keep throwing until you get 7 or the point
%   If you threw a 7, lose
%   If you threw the point, win

The words "if", "otherwise", and "keep" in the description kind of imply if, else, and while by their meanings, don't they?

Then you'd wrap those with more comments:

% Start off with 0 losses and 0 wins
% Play 100000 games of craps
% Each game of craps:
%   First throw
...

Translating from comments like that into code can be easier than keeping the whole design of your program in (your) memory. It can also help you identify if there are pieces of code you run frequently that may be useful helper functions.

[Robert Scott]

What I'm calculating is slightly different than what most people want to calculate (hence my difficulties). I'm trying to calculate the number of throws per hand.

% Start off with 0 losses, 0 wins, 0 rolls
% Play 100000 hands of craps
% Record number of rolls for each hand
% Each hand of craps:
%   First throw (come out roll)
%     If first throw is a 7 or 11, win, roll again
%     If first throw is a 2, 3, or 12, lose, roll again
%   Otherwise the point is equal to the first throw (point sequence)
%      Keep throwing until you get 7 or the point
%          If you throw a 7, lose, hand ends
%          If you threw the point, win, go back to beginning (come out roll)