Solve the problem by while loop

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sss dzu 2012-10-15

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评论： Image Analyst 2023-9-6

FIND THE SUM OF ALL ELEMENTS THE BETWEEN 5 AND 18 in the matrix BY WHILE LOOP. I know how to solve it by for loop, but when I try it by while loop, it does not run. Can anyone help me to correct it. Thank you. This is what I got

a=[10 18 12 8;
   1 8 115 9;
   35 12 21 13;
   25 0 16 5];
Re=0;
 i=1:4;
 j=1:4
 a (i,j)=5
while (a(i,j)<=18)
      Re= Re+ a(i,j);
end 
Re

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Niraj 2023-9-2

在 MATLAB Online 中打开

i=5;
sum=0;
while i<=18
    sum=sum+i;
    i = i + 1;
end
display(sum)

Image Analyst 2023-9-6

@Niraj, don't use "sum" as the name of your variable since it's the name of a built-in function that you don't want to overwrite. Also don't use i since it's the imaginary constant.

Anyway, your solution totally ignores "a" and so it doesn't work. Try again, or see my solution below.

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Answer 1

Image Analyst 2012-10-15

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https://ww2.mathworks.cn/matlabcentral/answers/50902-solve-the-problem-by-while-loop#answer_62032

编辑：Image Analyst 2012-10-15

在 MATLAB Online 中打开

Try

logicalIndex = 1;
while logicalIndex <= numel(a)
  Re = Re + a(logicalIndex);
  logicalIndex = logicalIndex + 1;
end

This is a good time/opportunity for you to learn about logical indexes versus regular indexes.

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sss dzu 2012-10-15

Thank you. I got the answer.

Image Analyst 2023-9-6

在 MATLAB Online 中打开

If this Answer solves your original question, then could you please click the "Accept this answer" link to award the answerer with "reputation points" for their efforts in helping you? They'd appreciate it. Thanks in advance. 🙂 Note: you can only accept one answer (so pick the best one) but you can click the "Vote" icon for as many Answers as you want. Voting for an answer will also award reputation points.

Since it's been 11 years, here is how you can do it via two different ways:

a=[10 18 12 8;
    1 8 115 9;
    35 12 21 13;
    25 0 16 5];
% Method 1: using logical index as a map for numbers in range:
logicalIndex = (a >= 5) & (a <= 18)
index = 1;
theSum1 = 0;
while index <= numel(a)
    if logicalIndex(index)
        % If it's in range, add it in.
        theSum1 = theSum1 + a(index);
        fprintf('Added in %d to the sum.  Current sum = %d.\n', a(index), theSum1)
    end
    index = index + 1;
end
theSum1
% Method 2: using lines index for numbers in range:
index = 1;
theSum2 = 0;
while index <= numel(a)
    inRange = (a(index) >= 5) & (a(index) <= 18);
    if inRange
        % If it's in range, add it in.
        theSum2 = theSum2 + a(index);
        fprintf('Added in %d to the sum.  Current sum = %d.\n', a(index), theSum2)
    end
    index = index + 1;
end
theSum2