How do I replace a specific value in vector after its been through a loop?

BRAWR is the sound that I make when I can't figure how this is supposed to work. For this assignment I'm meant to "declares a vector of numbers, A, and creates a new vector B, containing the cubes of the positive numbers in A. If an element is negative, put zero in the corresponding position in B. Your solution must use a loop to iterate through the vectors." however I can't make the corresponding position at b zero. heres what I have done so far.

A= [1, 2, -1, 5, 6, 7, -4, 3, -2, 0]; c=A for i=1:c if mod(c,2)==0 c=0 else c=c.*c.*c end end which gives me this c =

     1     8    -1   125   216   343   -64    27    -8     0

Answer 1

[Adam]

c = A;

will create an array c of length equal to A.

You don't then want to use

for i = 1:c

as a for loop condition as this doesn't make much sense. Seemingly it doesn't crash though I've never done it to know exactly what it will do.

i in your for loop is the index into the array so you should be doing something more like

c = zeros( size(A) );
for i = 1:numel(c)
    if someCondition
        c(i) = someValue
    end      
end

That is a general idea obviously, you have to fill in the relevant bits yourself.

I'm not sure why you are using 'c' when the questions asks for 'B', but that is a minor issue. Also I'm not sure what the question expects you to do with respect to initialisation of your B vector. If you initialise with zeros as I did then obviously you needn't do anything to explicitly put a zero in so I only included the clause for writing non-zero values.

This is a problem I would never use a for loop to solve in the first place so coursework insisting on you using a for loop is 'surprising' from a teaching perspective, but c'est la vie, that is what you are asked to do!