How to select only inverted faces

Imported a model form c4d but the faces are not calculated normal.
Ctrl+n did not do the trick. Is there a way to select only inverted faces to flip them.

some inverted face’s normal might need to be manually selected and inverted !

happy bl

If you’re using 2.8 remember that now Ctrl+n >> Shift+n

in 2.8 there is a way to show all inverted face directly
makes it easier to select these faces !

happy bl

Non manifold geometry. You’d need to fix this error first.
Create cycles material - mix red/blue color by Input - Geometry - Backfacing

Thanks solved the problem in the outliner there where mutliple objects which where the same.
Deleted them first then Ctrl+n solved the problem Blender 2.79b