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How to create a new variable for each iteration of a while loop?

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Matthew McLean
Matthew McLean el 26 de Abr. de 2017
Comentada: Stephen23 el 28 de Abr. de 2017
I am creating a library of books on matlab using a while loop. In the loop the user is asked for a title, author and number of pages. The user is then asked what would they like to do, and if they write add book, a new title author and number of pages should be given. This overwrites the original title author and number of pages and when typing list books, there is only every 1 book to list as only one exists. Obviously title_count does not work but that is the kind of thing I am looking for. also obviously the list books will not currently work, but I want to find a way to store them first and then I can figure that out. Here is my code currently;
a = input('What would you like to do: ', 's');
B = []
count = 1;
while true
if strcmp(a,'quit') == 1;
disp('Good-Bye')
return
elseif strcmp(a,'add book') == 1;
title = input('Title: ', 's');
author = input('Author: ', 's');
pages = input('Number of pages: ', 's');
fprintf('%s, %s, %s has been added to the library \n', title, author, pages)
title_count = title;
author_count = author;
pages_count = pages;
count = count + 1;
a = input('What would you like to do: ', 's');
elseif strcmp(a,'list books') == 1;
else
return
end
end
Please help :)
  2 comentarios
Stephen23
Stephen23 el 26 de Abr. de 2017
Editada: Stephen23 el 26 de Abr. de 2017
"How to create a new variable for each iteration of a while loop?"
That would be a really bad idea, because code that creates or accesses variable names dynamically is slow, buggy, hard to debug, hard to read... it is so bad, that the MATLAB documentation specifically advises to avoid doing that: "...this approach does not use the array processing power of MATLAB and is not recommended."
All of the experts here will advise you to use much simpler ,faster, and more efficient methods (aka better methods), such as using indexing or structure fields. You can also search this forum yourself for "dynamic variable names" and read some of the other threads that discuss this topic, or start by reading this tutorial:
Summary: use indexing. Probably a non-scalar structure would be the best choice for your situation.
Andrew Newell
Andrew Newell el 27 de Abr. de 2017
Someone flagged the previous comment as bullying, presumably because of the statement "That would be a really bad idea", but that statement is directed at the idea, not the person. And Stephen followed it up with a lot of useful information. A very helpful comment, I would say.

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Respuestas (1)

Andrew Newell
Andrew Newell el 26 de Abr. de 2017
Editada: Andrew Newell el 26 de Abr. de 2017
Structures are great for this kind of task (see struct). Here is an example script that assumes you have already created a book:
count = numel(book);
a = input('What would you like to do: ', 's');
while ~strcmp(a,'quit')
if strcmp(a,'add book') == 1
count = count + 1;
book(count).title = input('Title: ', 's');
book(count).author = input('Author: ', 's');
book(count).pages = input('Number of pages: ', 's');
fprintf('%s, %s, %s has been added to the library \n', ...
book(count).title, book(count).author, book(count).pages)
elseif strcmp(a,'list books') == 1
disp(book)
else
disp('Options are ''quit'', ''add book'' or ''list books''.')
end
a = input('What would you like to do: ', 's');
end
disp('Goodbye')
If you are starting with a new collection, you could initialize book with:
book = struct.empty;

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