A for loop that finds multiples of certain numbers in a given range

Question

Caroline F 2022-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/1665749-a-for-loop-that-finds-multiples-of-certain-numbers-in-a-given-range

评论： Image Analyst 2022-3-14

I am trying to create a for loop that finds all values in the range [1,100] that are also multiple of 3 or 5 and save these in a row vector labeled M1. It was suggested that I use mod()/rem() functions. I have been able to do this without a for loop, but when I try to use the for loop the answer is not in row vector form and there are a lot of blank answers.

x = [1:100];
i=1;
for k = 1:length(x)
    i=k(mod(k,3)==0)
    i=k(mod(k,5)==0)
end
M1=i

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Answer 1

David Hill 2022-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/1665749-a-for-loop-that-finds-multiples-of-certain-numbers-in-a-given-range#answer_912154

编辑：Image Analyst 2022-3-14

在 MATLAB Online 中打开

y=[];
for k = 1:100
    if mod(k,3)==0||mod(k,5)==5
      y=[y,k];
    end
end
y
y = 1×33
     3     6     9    12    15    18    21    24    27    30    33    36    39    42    45    48    51    54    57    60    63    66    69    72    75    78    81    84    87    90

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Garrett Viton 2022-3-14

This is not giving the multiples of 5 like 10, 20, 25, etc. What's the reasoning on this?

Image Analyst 2022-3-14

@Garrett Viton, it's because there is an error in the code. See my answer below.

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Answer 2

Image Analyst 2022-3-14

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https://ww2.mathworks.cn/matlabcentral/answers/1665749-a-for-loop-that-finds-multiples-of-certain-numbers-in-a-given-range#answer_917704

在 MATLAB Online 中打开

Try this:

% Construct a list of values to check.  Call it x.
x = 1 : 100;
% Initialize our output row vector to null.  Then we'll fill it up.
M1=[];
% Now check all the values in x to see if they are a multiple of 3 or 5.
for k = 1 : length(x)
    % Get this value of x.
    this_x = x(k);
    % Check the value to see if it's a multiple of 3 or 5.
    if (mod(this_x, 3) == 0) || (mod(this_x, 5) == 0)
        % If we get here, this_x is a multiple of 3 or 5.
        % Store the value in our output vector.
        M1 = [M1, this_x];
    end
end
M1
M1 = 1×47
     3     5     6     9    10    12    15    18    20    21    24    25    27    30    33    35    36    39    40    42    45    48    50    51    54    55    57    60    63    65