how do i use the if statement in a for loop

How do i use the IF statement to achieve my objective. I want the values of n for certain conditions to be output iteratively into a matrix and plotted (Julia sets)

c=-0.835 - 1i*0.232;
x=-2:0.005:2;
y=-2:0.005:2;
[X,Y]=meshgrid(x,y);
z=(X + Y*1i);
n_max=256;
b=10000;  %blowup parameter. stop an iteration when |z|>b.
a=(abs(z)>=10000);
m=(z.^n_max<10000)
n_matrix = zeros(800,800);
for n = 1:n_max
    f_z = z.^n + c;
    z = f_z ;
   if a    disp(n)
       if m disp (n)
      end
end

end
colormap prism(256)
pcolor(n);
shading flat;
axis('square','equal','off')

Answer 1

[Matt J]

This is literally what you asked for, but maybe not what you wanted.

ntable=1:nmax;

for n=1:nmax

    if condition_does_not_hold

     ntable(n)=nan;

   end

end

plot(ntable);

[Ejike]

thanks. i will just like clarification on (nan) and if condition holds.

[Ejike]

i actually need

if condition_holds ntable(n)= (n_for_ that_condition)

end