get the amount of colums from a structure in matlab

main.m
        ```matlab
        s = struct('field1', 1, 'field2', 'hello', 'field3', [1, 2, 3]);
        num_fields = numel(fieldnames(s));
        disp(num_fields);
        ```

        The output will be `3`, which is the number of fields in the struct `s`. Alternatively, you can use the `length` function like this:

        ```matlab
        num_fields = length(fieldnames(s));
        ```
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