[~, column_numbers] = find(Array)
[~, column_numbers] = find(Array == value)
Note: in the specific case where there is exactly one matching column per row, or you only want the first or last match per row, there are some alternatives that do not involve find(). They can involve processing the array multiple times, but in a way that can be automatically vectorized.
Caution: if you are working on the case where there is exactly one match per row, then chances are that you would consider the result of the above find() to be out of order, as it will not be ordered by increasing row. To order by increasing row use
[column_numbers, ~] = find(Array .');
This has to do with the order that MATLAB stores arrays.