how do i use the if statement in a for loop (corrected code)

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.^2)^n_max<10000)
n_matrix = zeros(800,800);
for n = 1:n_max
    f_z = z.^2 + 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')

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup