overwrite conditional function

Hi,

I’ve got code in my functions.php to add different class like this for example:

if ( is_page('11')) { echo 'class1'; } elseif ( is_page('12')) { echo 'class2'; } elseif ( in_category('4')) { echo 'class3'; }

and I want to overwrite class for a post in category 4. If I do this:
elseif (in_category('4') && is_single('106')) { echo 'class4'; }

But post 106 from category 4 keep class3, not class4 like I want. I want to know how I can tell WP to add one class for all posts in cat4 but add another class for post 106 that is in the same cat.

Thanks