Replacing part of an array with another

How do I replace the diagonal of one 2d array with the diagonal of another? The arrays have the same size.

Answer 1

[KSSV]

A = rand(4) ;
B = rand(4) ;

n = size(A,1);
A(1:(n+1):end) = diag(B) ; % repalce diagonal elements of A with diagonal elements of B