At common grammatical mistake is to use an N dash used instead of M dash (hyphen instead of a dash).
The following uses a hyphen or N dash (one single dash): My mother-in-law
The following uses an M dash, a long dash or two dashes to represent a break, interruption:
“I was on my way to the—Whoa, what are the neighbors doing? Honey, get the binoculars.”
More useful hyphen usage:
Hyphenate numbers, ages and descriptive words when they become a compound modifier which is often before a noun. There are a lot of exceptions. Below are all correct examples.
The tie is emerald green
The emerald-green tie
She is a twelve-year-old.
She is twelve years old.
Chapter Twenty-one up to Chapter Ninety-nine use hyphens.
Correct the Following:
“Don’t tell me what to do. I’m not your submissive, Fifty Shades of Grey bi-”
Maria said, “Hey! I only asked you to try the spank—o–matic.”
Chapter Two-hundred and Seventy two
My half full cup isn’t half-full.
I’ve been twenty-nine-years old for twenty one years.