Failure of the Continue command in a for-loop

Question

Robert Mason 2016-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/297851-failure-of-the-continue-command-in-a-for-loop

评论： Image Analyst 2016-7-31

I cannot get the continue command to work in for-loops. For instance, with the code:

q(1) = 1;
q(2) = 2;
q(3) = 3;
q(4) = 4;
q(5) = 5;
for j=1:5
    if j==2
        continue
    end
    qv=q
end

I expected the outcome of executing this code to be qv = [1 3 4 5], however the actual outcome is qv = [1 2 3 4 5].

Any suggestions as to how to get "continue" to work in this for-loop so that the output qv = [1 3 4 5] results?

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Answer 1

Star Strider 2016-7-31

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You’re not ‘building’ your ‘qv’ vector. You must also index ‘q’ since:

qv = q

sets ‘qv’ to all of ‘q’ in each iteration.

See if this does what you want:

q(1) = 1;
q(2) = 2;
q(3) = 3;
q(4) = 4;
q(5) = 5;
qv = [];                            % Initialise ‘qv’
for j=1:5
    if j==2
        continue
    end
    qv=[qv q(j)];                   % Concatenate New Value
end
qv
qv =
       1     3     4     5

One other observation:

q = 1:5;
q = [1 2 3 4 5];

will do the same assignment to ‘q’. The first creates a sequential vector, the second can contain any numbers you want (here consecutive, but they don’t have to be).

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Answer 2

Image Analyst 2016-7-31

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You constructed the for loop incorrectly. j takes on only the values 1 and 5. If you want it to take on the values 1,2,3,4 & 5, do this:

for j = 1 : 5

By the way, I fixed your code formatting. For your next post, read this link to learn how to format.

Also see this link to learn how you can step through code to see what values, such as your "j", take on at each line in your program.

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Robert Mason 2016-7-31

j = [1 5] does the same job in this case as j = 1:5 in my version of Matlab.

Unfortunately, I tried using j= 1:5 and it does not fix the original problem I described regarding the continue command.

Image Analyst 2016-7-31

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I seriously doubt that.

for j = [1 5]
  disp(j);
end
for j = 1 : 5
  disp(j);
end

shows

as expected. And I'm virtually 100% certain your version would too. What version do you have? I'd have to see a screenshot of you running the above code and getting something different to believe otherwise.

Anyway, Star corrected your two errors, one in constructing j and one in constructing qv.

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