How can I add a line to multiple files in a directory tree structure?

Question

Adding a line to multiple files in the same structure is not very hard, but I am stumped on how to do it over a possibly large directory tree structure. So lets say we have your project directory, which has hundreds of projects in it and you want to add a header to every *.c file. How can this be done? remember the files could be quite deep.

Answer 1

find ~/foldername -type f -name "*.c" -exec sed -i '1 i addtexthere' {} \;