How to make a for loop that sums all the odd values in the array?

Question

Kristen O'Mara 2018-2-22

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评论： Khondaker 2023-4-2

I need to make a for loop that sums all the odd values in an array from 1 to userNum. This is what I have so far:

   function [summedValue] = OddSum(userNum)
     for i = 1:2:userNum
        summedValue = sum(i);
     end

When the user number is 5 I'm getting 5 as an output when I should be getting 9. I thought when I used the for-loop it made an array [1, 3, 5] because of the counter equalling 2. Then when I typed summedValue = sum(i) I thought it would take the sum of all the elements of the array.

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Jan 2018-2-24

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@John BG: The explanation is:

I need to make a for loop that sums all the odd values

Then omitting the loop is interesting (and has been mentioned in my answer already), but not wanted.

John BG 2018-2-25

Jan Simon: sometimes people coming from C++ and other languages do not realise how compact MATLAB can be.

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Answer 1

James Tursa 2018-2-22

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Initialize your summing variable prior to the loop:

summedValue = 0;

Then inside the loop, add to it:

     for i = 1:2:userNum
        summedValue = summedValue + __________;
     end

You need to fill in the blank with appropriate code.

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Anita Osoh 2020-11-1

what would u enter??

Khondaker 2023-4-2

Shall I enter userNum? But still it didn't work

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Answer 2

Jan 2018-2-22

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编辑：Jan 2018-2-24

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Do you know the debugger already? https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html

You can set a breakpoint in the code and step through it line by line. This let you see, what's going on. You can examine directly, that sum(i) replies i, because it is a sum of a single element. Then summedValue is overwritten in each iteration. See James' answer.

By the way: While you are wanted to use a loop, you can do this much nicer in Matlab:

v = 1:2:userNum

Now you have a vector of the numbers and sum() adds all elements of a vector.

And of course, Gauss would do this with a tiny formula instead of processing all elements individually.