Plotting a variable after initally guessing the value

I am trying to use a numerical method to find out the answer to a function. I use an initial guess and iterate until the answer is correct. I am trying to plot Zg vs. D, but cannot figure out how to save Zg after each iteration of D.

Zg = 1; D = 1:1:20; error = 5; A = 100; for i = 1:length(D)

    while error >= 1

        if D(i) <= 10

            P = 5*D(i) * Zg;

        else 

            P = D(i) * Zg;

        end

        error = ((A-P)/A)*100;

        Zg = Zg +1;
    end

end

[Rik]

You can index Zg as well. Also, you shouldn't overwrite the internal function error with a variable.