Control flow of loop

for i = 2:41616 if x(i-1) < 0.5 x(i) = a*x(i-1); elseif x(i-1) >= 0.5 x(i) = a*(1- x(i-1));

    end
end

I would like to change each of the x(i) values using the below given statement and i need an 1D vector sy. So please help me where should i place this code statement to find "sy" in the above code. Because i am unsure about the control flow. "sy = mod((x(i) * (10^10)),256);"