find is essentially the command line tool for traversing the file system hierarchy recursively. It's got a million options, e.g. whether to follow symlinks, depth, file/directory/device/.., user, group, change time and many more. When you use grep -r, it only does the most common thing which is to just go over all the files. If you want something more "fancy", you can use find, e.g.:

  $ find -name '*.c' -type f -exec grep printf '{}' +