How can I change the pixel value of central row and column of an image?

I have already used one method but I want to use another method without using "for loop". My code is...

 a = imread('pic.jpg');
[r,c]=size(a);
centerRow = round(r/2);
centerColumn = round(c/2);
 for i=1:r
   for j=1:c
     if(i==centerRow || j==centerColumn)
        a(i,j) =255;  
     end 
   end
end
imshow(a);

Answer 1

[KSSV]

for loop is not required........

a = imread('pic.jpg');
[r,c]=size(a);
centerRow = round(r/2);
centerColumn = round(c/2);
a(centerRow,centerColumn,:) =255;
imshow(a);

[Shakir Ishaq]

Thank you for helping me but I want result like this.

The above code does not give result like this.