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RE: Repeating bug (error: subscript indices must be either positiveinteg

From: Allen.Windhorn
Subject: RE: Repeating bug (error: subscript indices must be either positiveintegers or logicals)
Date: Wed, 27 Apr 2011 15:15:35 -0500

From: address@hidden On Behalf Of ragan2328
 > I've had yet another problem dealing with an infinite loop I was
> hoping you could help out with. I have a feeling this one is a quick
> fix. Additionally, the details of the assignment were to create a
> generator that outputted a password, but that it must have at least
> one uppercase letter, one lowercase letter, one digit, and the first
> character must be a letter.
> Now, the problem I've been having was that the password never seems
> to pass the requirements in PassCheck, resulting in an infinite
> loop. I'm reattaching my revised programs, I hope you can help me
> out on this one. Thanks so much again.
I didn't look for your bug, but you might try a different approach.  I made
a similar password generator, but what I would recommend is to first
generate a password of (say) n all lower-case letters.  Randomly
change the case of the first letter with a probability of 0.5:
lower1 = 1;
if (rand() > 0.5)
  password(1) = toupper(password(1);
  lower1 = 0;
Take the next k characters where k is a random integer between 1 and
(n-3) and change them to random digits:
n = length(password);
k = floor(rand()*(n-3)+1);
digs = int2str(floor(10*rand(k,1)));
password(2:k+1) = digs;
Maybe the value of k should be biased or limited to a lower number since
there aren't as many digits as letters.
Take the last (n-k-1) characters and change a random number of them
to upper case (but not all, unless the first character is lower case):
m = floor(rand()*(n-k-2+lower1));
password(k+2:k+2+m) = toupper(password(k+2:k+2+m);
I haven't tested this exhaustively so it wants some careful counting in
case I'm off by one somewhere.  m should range from 0 to two less
than the remaining number of letters, or one less if the first letter is lower
Then scramble the last n-1 characters:
password(2:n) = shuffle(password(2:n));
I wrote a shuffle function below but there is probably already one out
there somewhere.
function chars = shuffle(str)
%shuffle(str) Return shuffled string
% Randomly permute characters of string and return shuffled version
  chars = str;
  for idx = 1:length(str)
    swp = randpick(1:length(str));
    tmp = chars(idx);
    chars(idx) = chars(swp);
    chars(swp) = tmp;
function k = randpick(rng)
% Select a random integer within range
  k = floor(rand()*length(rng)+1);

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