why isn't image changing when it is supposed to?

THis one has me stumped for two days straight. It seems like it should be the easiest thing in the world, but there's something I'm just not getting.

I want the image to change to the next image every time bb = 3, or fstep/2, and stay on that image otherwise. There will be other images coming in at different places, so I can't just adjust the starting point, it has to change at bb=fstep/2 exactly. Nothing I code will do this, it keeps changing only at bb=1 instead. I'm mystified, can anybody see what's wrong and can suggest a change with as little modification to the original code as possible?

clear all
clf
fpath1 = '/Users/owner/Documents/MATLAB1/';
addpath(fpath1);
pI1 = 1 + [0, 1, 2];
pIsiz = size(pI1,2);
IB = {'T5 01.jpg'; 'T5 02.jpg'; 'T5 03.jpg'};
fI1B = {IB{pI1(1:pIsiz)}};
fstep = 3; % FRAME STEPS BETWEEN EACH IMAGE ----------------
bbm = [(fstep/2)+1:fstep 1:fstep/2];
fstep = fstep * 2;
cc = 1;
for aa = 1:3
    astr = num2str2023(aa); % FILE NAME INCREMENT VALUE
    I2 = imread(fI1B{aa});
    for bb = 1:fstep
        [aa bb cc]
        if mod(cc,fstep) == fstep/2
            I2 = imread(fI1B{aa});
            fI1B{aa}
        end
        
        astr = num2str2023(aa); % FILE NAME INCREMENT VALUE
        bstr = num2str2023(bb);
        imf12 = [fpath1,'MTEST ' astr,' ', bstr, ' 2023.tif'];
        imwrite(I2, imf12, 'tif', 'Resolution', 720);
        cc = cc + 1;
    end
end

Answer 1

[Walter Roberson]

cc starts at 1.

fstep is 3.

mod() of an integer by 3 is going to be an integer.

You compare that integer to fstep/2 which is 3/2 which is a non-integer.

Therefore the mod() can only come true if at some point you increment c by a non-integer. But you never do, you only increment it by 1.

[mark palmer]

thanks for your response!

fstep is 6 (fstep * 2) by the time it reaches the loop. bbm can be ignored

Answer 2

[mark palmer]

I figured out the issue, thanks.