Never ending while-loop

Question

Nicle Davidson 2021-9-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1451114-never-ending-while-loop

评论： Nicle Davidson 2021-9-12

采纳的回答： DGM

在 MATLAB Online 中打开

I have a while-loop that I can not get out of.

What I get out of my test is that:

we are in the while-loop

I turn the wheels one step-Pos == 1

we are in the while-loop

I turn the wheels one step-Pos == 1

we are in the while-loop

I turn the wheels one step-Pos == 1

we are in the while-loop

I turn the wheels one step-Pos == 1

we are in the while-loop

I turn the wheels one step-Pos == 1

etc.

It shows that my code goes into the while-loop, where it says 'we are in the while-loop', and then it goes into the if statement, checks to which position we are, then it do the strcmp, and if true goes into it, if not goes to else, it should however make the Pos variable 0 when has been to Pos 1 and vice versa.

howerver it goes into the if for Pos 1 and strcmp somehow is false and it goes to else, and it does the same again.

could I stop this while loop and do what is the goal with it?

notFound is used to stop this while looping, but maybe I have put it wrong place?

*I need to go first to Pos 1 test and second time to Pos 0, and change from 0 to 1 againg and back to 0 next time. (interchangeable)

variabel = 'test';
LW= 'azyxwvutsrqponmlkjihgfedcb';
MW= 'acedfhgikjlnmoqprtsuwvxzyb';
RW= 'abcdefghijklmnopqrstuvwxyz';
dW='';
notFound = 1;
Pos=1;
for p=1:length(variabel)
        while notFound == 1
        disp('we are in the while-loop');
            if Pos == 1
                if strcmp(LW(1),variabel(p))
                    disp('Is in pos 1!!\n');
                    dW= append(dW, RW(1));
                    notFound = 0;
                    Pos=0;
                else
                    disp('I turn the wheels one step-Pos == 1');
                    RW = circshift(RW,-1); % does the same thing as above
                    disp(RW);
                    %counterclockwise
                    MW = circshift(MW,1); % does the same thing as above
                    disp(LW);
                    %clockwise
                    LW = circshift(LW,-1); % does the same thing as above
                    disp(LW);
                end
            else
                if strcmp(MW(1),variabel(p))
                    disp('is in pos 0!!\n');
                    dW= append(dW, RW(1));
                    notFound = 0;
                    Pos=1;
                else
                    disp('I turn the wheels one step-Pos == 0');
                    RW = circshift(RW,-1); % does the same thing as above
                    disp(RW);
                    %counterclockwise
                    MW = circshift(MW,1); % does the same thing as above
                    disp(LW);
                    %clockwise
                    LW = circshift(LW,-1); % does the same thing as above
                    disp(LW);
                end
            end
        end
end

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Answer 1

DGM 2021-9-11

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1451114-never-ending-while-loop#answer_785179

编辑：DGM 2021-9-11

在 MATLAB Online 中打开

There are a few problems. LW(1) will never match variabel, since they're different lengths. The first 3 characters of LW will never match variabel, since all that's going on here are circular shifts, and LW does not contain that substring.

pT='abc';
variabel = pT;
LW= 'azyxwvutsrqponmlkjihgfedcb';
MW= 'acedfhgikjlnmoqprtsuwvxzyb';
RW= 'abcdefghijklmnopqrstuvwxyz';
dW='';
notFound = 1;
Pos=1;
while notFound == 1
	%disp('we are in the while-loop');
	if Pos == 1
		
        % Pos will never be changed
		if strcmp(LW(1:numel(variabel)),variabel) % need to test at least the same number of chars
			%disp('Is in pos 1!!\n');
			dW= append(dW, RW(1));
			notFound = 0;
			Pos = 0;
		else
			%disp('I turn the wheels one step-Pos == 1');
			
%			store=RW;
% 			for j=1:(length(RW)-1)
% 				RW(j)=RW(j+1);
% 			end			
%			RW(end)=store(1);
			RW = circshift(RW,-1); % does the same thing as above
			
%			store=MW;
%			store(1)=MW(end);
% 			for m=1:(length(MW))
% 				store(m+1)=MW(m);
% 			end
%			MW=store(1:end-1);
			MW = circshift(MW,1); % does the same thing as above
			
%			store=LW;
% 			for n=1:(length(LW)-1)
% 				LW(n)=LW(n+1);
% 			end
%			LW(end)=store(1);
			LW = circshift(LW,-1); % does the same thing as above
			
		end
	else
        % all this can be simplified in a similar manner
	end
end

Even if the substring under test is something like [LW(1) MW(1) RW(1)], that won't match variabel either, since LW and RW are shifted in the same direction and no occurrence of ['a' MW(1) 'c'] will ever occur.

As the comment mentions, the second part simplifies as well. Depending on what the actual goals are, the entire thing should simplify further yet. For example, if Pos always is initialized to 1, then the whole second part of the loop is unused and can be removed. This is because the only time Pos is set to 0 is when the loop exits.

pT='abc';
variabel = pT;
LW= 'azyxwvutsrqponmlkjihgfedcb';
MW= 'acedfhgikjlnmoqprtsuwvxzyb';
RW= 'abcdefghijklmnopqrstuvwxyz';
dW='';
notFound = 1;
while notFound == 1
	if strcmp(LW(1:numel(variabel)),variabel) % need to test at least the same number of chars
		dW= append(dW, RW(1));
		notFound = 0;
	else
		RW = circshift(RW,-1);
		MW = circshift(MW,1);
		LW = circshift(LW,-1);
	end
end

But of course, I don't know what this is really supposed to be doing.

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Nicle Davidson 2021-9-11

在 MATLAB Online 中打开

First of all, thank you for making me aware of circshift(), it looks very much more effective than what I had tried to code for it.

then, if strcmp(LW(1:numel(variabel)),variabel) still is not able to do the check, even when variable is 'a' and the first word is 'a' in the string of words.

So I understand that the problem exists in the 'if' statement,

so I think I should ask how could I compare this so it could compare the first word with another string.

Say I have a string called pT= 'test'

and I have a string such as shown above like: LW= 'azyxwvutsrqponmlkjihgfedcb';

As I knew before strcmp(,) would have been able to do this

but now I see there is some complications.

I think I should go a bit back in the code (which is not long) to tell the history of LW

I have the strings:

pT='test';
fS = 'abcdefghijklmnopqrstuvwxyz';
sS = 'acedfhgikjlnmoqprtsuwvxzyb';
vS = 'azyxwvutsrqponmlkjihgfedcb';
spokes = perms({fS, sS, vS});%I permutate them
for q=1:6 %then in a for-loop of 6 times
                    LW=  spokes(q:1);
                    MW=  spokes(q:2);
                    RW=  spokes(q:3);
                    %then I send LW, MW, RW, pT in a function to another page,
                    %which has the code above.
                    %that is where the if statement wants to comare and see
                    %if for example what is in LW this time, is the first word in LW now 
                    % 't'? ( I have added the for loop for taking a word
                    % from pT at a time.
                    %please see the update of the code above
                    
                    %then do the function mention above (in the first place
                    %I wrote the question) here 
                    answer =anotherPage(ML, RW, LW, pT);
                
end

The while loop still does not stop, because notFound = 0 is in the if statement, and the if statement does not fuction, is there any solution for the functionality of the if-statement with the contition in the code I explained here?

DGM 2021-9-12

编辑：DGM 2021-9-12

在 MATLAB Online 中打开

Let's see if this gets us closer:

variabel = 'test';
LW= 'azyxwvutsrqponmlkjihgfedcb';
MW= 'acedfhgikjlnmoqprtsuwvxzyb';
RW= 'abcdefghijklmnopqrstuvwxyz';
dW='';
% 1 means LW; 0 means MW
% behavior should alternate between the two
Pos = 1;
for p=1:length(variabel)
    % i inverted the logic here so the flag could be used for multiple things
	isDone = false; % reset the flag inside the loop
    while ~isDone
		if Pos == 1
			isDone = strcmp(LW(1),variabel(p));
		else
			isDone = strcmp(MW(1),variabel(p));
		end
		
		if isDone
			fprintf('Finished in pos %d!!\n',Pos);
			dW = append(dW, RW(1));
			Pos = xor(Pos,1); % toggle 
			disp([RW; MW; LW])
		else
			fprintf('I turn the wheels one step (in pos %d)\n',Pos);
			RW = circshift(RW,-1); % shift left (ccw)
			MW = circshift(MW,1); % shift right (cw)
			LW = circshift(LW,-1); % shift left (ccw)
		end
	end
end
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
Finished in pos 1!!
hijklmnopqrstuvwxyzabcdefg
uwvxzybacedfhgikjlnmoqprts
tsrqponmlkjihgfedcbazyxwvu
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
I turn the wheels one step (in pos 0)
Finished in pos 0!!
yzabcdefghijklmnopqrstuvwx
edfhgikjlnmoqprtsuwvxzybac
cbazyxwvutsrqponmlkjihgfed
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
I turn the wheels one step (in pos 1)
Finished in pos 1!!
ijklmnopqrstuvwxyzabcdefgh
suwvxzybacedfhgikjlnmoqprt
srqponmlkjihgfedcbazyxwvut
I turn the wheels one step (in pos 0)
Finished in pos 0!!
jklmnopqrstuvwxyzabcdefghi
tsuwvxzybacedfhgikjlnmoqpr
rqponmlkjihgfedcbazyxwvuts

Nicle Davidson 2021-9-12

Thank you, your code writing is very good.

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Never ending while-loop

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Never ending while-loop

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