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Whenever I run this function, all is good if A(i)==N. However when it is not found, the function seems to run super slowly that i never end up getting the output of 0. Do I need to preallocate somewhere? If so, what would it be?

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champions2015 2017-9-11

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https://ww2.mathworks.cn/matlabcentral/answers/356146-whenever-i-run-this-function-all-is-good-if-a-i-n-however-when-it-is-not-found-the-function-see

评论： John D'Errico 2017-9-11

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"Write a function, Finder, that receives an array of numbers A and a number N and returns the position of N within the array A or the value zero if N is not present within A."

function pos=Finder(A,N)
found=false;
while ~found
    for i=1:length(A);
        if A(i)==N;
            found=true;
            break
        end
    end
end
if found
    pos=i;
else
    pos=0;
end
end

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回答（1 个）

Walter Roberson 2017-9-11

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You should use either a while loop or a for loop, but not both.

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José-Luis 2017-9-11

On top of what Walter said, in your code, if it never gets found, your condition never gets set to true and you never break out of the while loop.

John D'Errico 2017-9-11

The real question is, why not just use ismember?

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