Both book and movie Jacks are published writers and English teachers. But book Jack isn't writing a novel. Instead, he's writing a play called The Little School, which is loosely based on Jack's previous job at a New England prep school from where he was fired for beating up a student. George Hatfield had slashed Jack's tires after Jack cut him from the debate team, and in a sober rage, Jack almost killed the kid. But once the evil in the Overlook begins taking hold of Jack, it leaves him a strange gift. After finding a scrapbook of articles about the sordid history of the hotel's connections to the mob, human trafficking, murder, and suicide, Jack ditches the play and decides he's going to write a tell-all about the Overlook, instead.
In The Shining movie, Jack is writing a novel that turns out to be the phrase "all work and no play makes Jack a dull boy" written over and over again on hundreds of pages. This isn't in King's book, but Kubrick does give a small nod to the scrapbook Jack finds in the novel, as there's a huge tome of clippings next to Jack's typewriter in the main Overlook lobby. However, in the book, Jack doesn't write in the lobby at all, but rather in his caretaker quarters.
His writing aside, Jack in the novel is open about his alcoholism, as well as hurting his son when he was drunk, confessing that he broke Danny's arm by accident to several people in bouts of remorse. In the film, Jack dislocates Danny's shoulder instead of breaking it, and he insists it really wasn't his fault. After all, Danny shouldn't have been messing with his stuff.
