MATLAB: Can I assign values to an array in a diagonal direction from a reference point on that array

array chess matrix diagonal board for loop

If I have an array of size NxN,called X, and I count through it using an (i,j) for loop like this
 for i = 1:N
    for j = 1:N
and im looking for a value in it like this
if(X(i,j) == 1)
I want to start where I find a 1 and change the diagonal lines around it to an 8. So far ive tried code similar to this and many things like it but it doesnt seem to work how I envision it
for i = 1:N
    for j = 1:N
        if(X(i,j) == 1)
            X(i+1,j+1) = 8;
            X(i-1,j-1) = 8;
            X(i+1,j-1) = 8;
            X(i-1,j+1) = 8;
       end  
    end
end
I want the outcome to be something like
0 0 0 0 0
0 0 0 0 0
0 0 1 0 0
0 0 0 0 0
0 0 0 0 0
this turns into this
8 0 0 0 8
0 8 0 8 0
0 0 1 0 0
0 8 0 8 0
8 0 0 0 8

Best Answer

Perhaps:
X = [...
0 0 0 0 0 0
0 0 0 0 0 0
0 0 1 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 0 0
0 0 0 0 0 0
0 0 0 0 0 0
];
[R,C] = find(X);
for k = 1:numel(R)
    r = R(k);
    c = C(k);
    X([r-1,r+1],[c-1,c+1]) = 8;
    X([r-2,r+2],[c-2,c+2]) = 8;
end
giving:
>> X
X =
   8     0     0     0     8     0
   0     8     0     8     0     0
   0     0     1     0     0     0
   0     8     0     8     0     0
   8     0     0     0     8     0
   0     8     0     0     0     8
   0     0     8     0     8     0
   0     0     0     1     0     0
   0     0     8     0     8     0
   0     8     0     0     0     8
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