Lines that end with a backslash character ``\'' and new-line
are joined with the next line by deleting the backslash
and the new-line characters, so that each line in the source
file is a logical line.
This occurs (in translation phase 2) before input is divided into tokens.
Lines beginning with #
are preprocessing directives.
Spaces and tabs may appear before and after the #.
Each preprocessing directive must
appear on a logical line by itself.