Plz explain this code ? why is the loop required , and how parameters are restricted in the 4th last line of the code ?

if true
  % code
x=0:255; 
for i=1:20    
   if i==1;y=x;
   else x=[x;y]; 
  end
end
p= 100*ones(16,200)
x(28:27+16,29:28+200)=p;
imshow(uint8(p))
figure, imshow(uint8(x))
end