Sometimes when writing code, we wish to embed a note to ourselves. Every programming language contains a facility for writing "comments". A comment is a line of code (or part of a line) that is intended for the human author to read, and for the computer to completely ignore.
Ruby uses the # sign to indicate the beginning of a comment.
All characters after the # sign are ignored through the end
of the line:
Notice here that Ruby ignores the note "meters/second per second", which would have otherwised cause a syntax error.
irb(main)> gravity = 9.8 # meters/second per second
=> 9.8
Try removing the # to see what would happen!
Inside quotation marks as part of a text fragment, the # is not treated as the beginning of a comment:
irb(main)> tweet = "Programming is fun! #ruby #programming"
=> "Programming is fun! #ruby #programming"