How would I use loops to set certain values in a martix to 0?

I want to make a function that turns every value but the values in a diagonal shape for a matrice.

function [X] = threeMatrices(matrice)

X = matrice;
X(1,2) = 0;
X(1,3) = 0;
X(2,1) = 0;
X(2,3) = 0;
X(3,1) = 0;
X(3,2) = 0;

end

But this doesn't work with matrices of random sizes. Am I supposed to use a loop or anything?

Answer 1

[Benjamin]

X(~eye(size(X))) = 0;

[Kylenino Espinas]

If I wanted to do the opposite of the diagonal and do everything but it, how would I change it?