Count lines of all files in a folder

This will count lines of every file in the folder, and give aggregate number of lines as well

find /path/to/dir -type f -name '*' | xargs wc -l

[Specifying the extension of file ]
find /path/to/dir -type f -name '*.c' | xargs wc -l

[This will lists the files in that folder with .c extension]
find /path/to/dir -type f -name '*.c'