How to find multiples of 3 in a vector using a for loop?

Hello all, I am trying to use a for loop to find the multiples of 3 in a random vector of size (20,1) and then assign these values to a new column vector. I am new to using for loops and am searching for guidance. I currently have this

X = rand(20,1);
i = 1;
for t = 1:length(X)
    i = t(mod(t,3)==0)
end 
T4 = i

I am not sure if this is even close, but any feedback would be greatly appreciated!

Thank you

[Walter Roberson]

rand() returns floating point numbers in the range 0 to 1 (excluding 0 and excluding 1), and those will never be multiples of 3. Consider using randi() instead.

[Bennett Moore]

You are correct! thank you very much

Answer 1

[Walter Roberson]

You can use the general outline:

initialize output to be empty
loop over individual members of the input
  test if the individual member meets some condition
    if it does, add the individual member to the end of the output
end of loop

[Bennett Moore]

This helps a lot, thank you!

Answer 2

[Stephan]

Hi,

there is no need to use a for loop to achieve what you want. If you want to understand for loops use them, but here is a smarter way:

x = randi(15,20,1)
y = x(mod(x,3)==0)

Best regards

Stephan

[Walter Roberson]

Looks like it is a homework assignment to me, in which case using a "for" loop is probably mandatory.

[John D'Errico]

Yes, a for loop is surely indicated. Nevertheless, it is always good to see the other side, to learn where you want to go in the future as MATLAB skills grow.