How to convert from a for loop to a while loop

I need to modify the set of codes below to a while loop

[Steven Lord]

What have you tried so far?

[James Tursa]

Why do you need this converted? Is this homework? Why not get rid of the loop entirely and vectorize this operation?

[Yuqing Zhu]

I do like this from lecture note, but doesn't work well. Anything wrong happened?

Vector = [3 -3 2 -6 1 -9];
Index = 1;
while Index <= length(Vector);
    if(Vector(Index)<0);
        continue
    else
        Vector(Index) = Vector(Index) * 2;
    end
    Index=Index+1;
end
disp(Vector)

Answer 1

[James Tursa]

Your loop doesn't work because the "continue" statement skips over the Index=Index+1 statement. You need to rewrite things without skipping over that statement ... e.g., maybe try to rewrite your if-then-else stuff so that you do not use a "continue" statement. (Hint: What happens to your logic if you simply comment out that "continue" statement?)

[Yuqing Zhu]

This question is from my review session. Use another way to do the same job maybe should be while loop. I have no idea to do the same job

[James Tursa]

See my hint about how to get your while loop version working. Or see Dave Barry's one-liner.

Answer 2

[David Barry]

This does not need to be any kind of loop. You should learn about logical indexing in MATLAB. This can be done with one line of code.

Vector(Vector >=0) = Vector(Vector >=0) * 2;

https://uk.mathworks.com/help/matlab/math/matrix-indexing.html?refresh=true#responsive_offcanvas